Update:  I booted the machine with a NetBSD-4.0_BETA kernel on Aug 28  
in SMP mode using a kernel configuration that would trigger the  
problem with a 3.x kernel with in a day or to.

With the exception of one UPS failure related reboot, the machine has  
been stable.

Conclusion: Whatever the problem was under 3.x was fixed in 4.0

BTW, this is a Tylan K8S Pro motherboard (S2882G3NR).  It needs  
'options ACPI_SCANPCI' to find all PCI busses.

For my part, the PR can be closed at the discretion of the kern-bug- 
people.

Boot log, for completeness sake:

NetBSD 4.0_BETA (PLANIX.MPACPI) #7: Mon Aug 28 10:16:18 EDT 2006
         root@woffi.wrede.pvt:/m5/netbsd-4.0/obj.i386/sys/arch/i386/ 
compile/PLANIX.MPACPI
total memory = 1022 MB
avail memory = 997 MB
timecounter: Timecounters tick every 10.000 msec
timecounter: Timecounter "i8254" frequency 1193182 Hz quality 100
timecounter: selected timecounter "i8254" frequency 1193182 Hz  
quality 100
BIOS32 rev. 0 found at 0xfd5c0
mainbus0 (root)
cpu0 at mainbus0: apid 0 (boot processor)
cpu0: AMD Unknown K7 (Athlon) (686-class), 2009.35 MHz, id 0xf5a
cpu0: features 78bfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR>
cpu0: features 78bfbff<PGE,MCA,CMOV,PAT,PSE36,MPC,MMX>
cpu0: features 78bfbff<FXSR,SSE,SSE2>
cpu0: "AMD Opteron(tm) Processor 246"
cpu0: calibrating local timer
cpu0: apic clock running at 200 MHz
cpu1 at mainbus0: apid 1 (application processor)
cpu1: starting
cpu1: AMD Unknown K7 (Athlon) (686-class), 2009.26 MHz, id 0xf5a
cpu1: features 78bfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR>
cpu1: features 78bfbff<PGE,MCA,CMOV,PAT,PSE36,MPC,MMX>
cpu1: features 78bfbff<FXSR,SSE,SSE2>
cpu1: "AMD Opteron(tm) Processor 246"
ioapic0 at mainbus0 apid 2 (I/O APIC)
ioapic0: pa 0xfec00000, version 11, 24 pins
ioapic1 at mainbus0 apid 3 (I/O APIC)
ioapic1: pa 0xdf200000, version 11, 4 pins
ioapic2 at mainbus0 apid 4 (I/O APIC)
ioapic2: pa 0xdf201000, version 11, 4 pins
acpi0 at mainbus0: Advanced Configuration and Power Interface
acpi0: using Intel ACPI CA subsystem version 20060217
acpi0: X/RSDT: OemId <PTLTD ,  RSDT  ,06040000>, AslId < LTP,00000000>
acpi0: SCI interrupting at int 9
acpi0: fixed-feature power button present
timecounter: Timecounter "ACPI-Fast" frequency 3579545 Hz quality 1000
timecounter: selected timecounter "ACPI-Fast" frequency 3579545 Hz  
quality 1000
ACPI-Fast 24-bit timer
mpacpi: could not get bus number, assuming bus 0
ACPI Object Type 'Processor' (0x0c) at acpi0 not configured
ACPI Object Type 'Processor' (0x0c) at acpi0 not configured
ACPI Object Type 'Processor' (0x0c) at acpi0 not configured
ACPI Object Type 'Processor' (0x0c) at acpi0 not configured
acpibut0 at acpi0 (PNP0C0C): ACPI Power Button
PNP0C01 [System Board] at acpi0 not configured
PNP0A03 [PCI/PCI-X Host Bridge] at acpi0 not configured
PNP0C02 [Plug and Play motherboard register resources] at acpi0 not  
configured
PNP0C02 [Plug and Play motherboard register resources] at acpi0 not  
configured
PNP0000 [AT Interrupt Controller] at acpi0 not configured
attimer1 at acpi0 (PNP0100): AT Timer
attimer1: io 0x40-0x43 irq 0
PNP0200 [AT DMA Controller] at acpi0 not configured
pcppi1 at acpi0 (PNP0800)
pcppi1: io 0x61
midi0 at pcppi1: PC speaker (CPU-intensive output)
sysbeep0 at pcppi1
PNP0B00 [AT Real-Time Clock] at acpi0 not configured
npx0 at acpi0 (PNP0C04)
npx0: io 0xf0-0xf1 irq 13
npx0: using exception 16
PNP0A05 [Generic Container Device] at acpi0 not configured
pckbc0 at acpi0 (PNP0F13): aux port
pckbc0: irq 12
pckbc1 at acpi0 (PNP0303): kbd port
pckbc1: io 0x60,0x64 irq 1
com0 at acpi0 (PNP0501-1)
com0: io 0x3f8-0x3ff irq 4
com0: ns16550a, working fifo
com1 at acpi0 (PNP0501-2)
com1: io 0x2f8-0x2ff irq 3
com1: ns16550a, working fifo
com1: console
fdc0 at acpi0 (PNP0700-1)
fdc0: io 0x3f0-0x3f5,0x3f7 irq 6 drq 2
lpt0 at acpi0 (PNP0401-2)
lpt0: io 0x378-0x37f,0x778-0x77f irq 7 drq 3
PNP0C0F [PCI interrupt link device] at acpi0 not configured
PNP0C0F [PCI interrupt link device] at acpi0 not configured
PNP0C0F [PCI interrupt link device] at acpi0 not configured
PNP0C0F [PCI interrupt link device] at acpi0 not configured
PNP0C0F [PCI interrupt link device] at acpi0 not configured
PNP0C0F [PCI interrupt link device] at acpi0 not configured
PNP0C0F [PCI interrupt link device] at acpi0 not configured
PNP0C0F [PCI interrupt link device] at acpi0 not configured
PNP0A03 [PCI/PCI-X Host Bridge] at acpi0 not configured
pcppi1: attached to attimer1
pckbd0 at pckbc1 (kbd slot)
pckbc1: using irq 1 for kbd slot
wskbd0 at pckbd0 mux 1
pci0 at mainbus0 bus 0: configuration mode 1
pci0: i/o space, memory space enabled, rd/line, rd/mult, wr/inv ok
NVIDIA nForce4 Memory Controller (miscellaneous memory, revision  
0xa3) at pci0 dev 0 function 0 not configured
pcib0 at pci0 dev 1 function 0
pcib0: NVIDIA nForce4 PCI-ISA bridge (rev. 0xa3)
NVIDIA nForce4 SMBus (SMBus serial bus, revision 0xa2) at pci0 dev 1  
function 1 not configured
ohci0 at pci0 dev 2 function 0: NVIDIA nForce4 USB Host Controller  
(rev. 0xa2)
LUS0: Picked IRQ 20 with weight 0
ohci0: interrupting at ioapic0 pin 20 (irq 10)
ohci0: OHCI version 1.0, legacy support
usb0 at ohci0: USB revision 1.0
uhub0 at usb0
uhub0: NVIDIA OHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub0: 10 ports with 10 removable, self powered
ehci0 at pci0 dev 2 function 1: NVIDIA nForce4 USB2 Host Controller  
(rev. 0xa3)
LUS2: Picked IRQ 21 with weight 0
ehci0: interrupting at ioapic0 pin 21 (irq 11)
ehci0: BIOS has given up ownership
ehci0: EHCI version 1.0
ehci0: companion controller, 4 ports each: ohci0
usb1 at ehci0: USB revision 2.0
uhub1 at usb1
uhub1: NVIDIA EHCI root hub, class 9/0, rev 2.00/1.00, addr 1
uhub1: 10 ports with 10 removable, self powered
viaide0 at pci0 dev 6 function 0
viaide0: NVIDIA nForce4 IDE Controller (rev. 0xf2)
viaide0: bus-master DMA support present
viaide0: primary channel configured to compatibility mode
viaide0: primary channel ignored (disabled)
viaide0: secondary channel configured to compatibility mode
viaide0: secondary channel interrupting at ioapic0 pin 15 (irq 15)
atabus0 at viaide0 channel 1
viaide1 at pci0 dev 7 function 0
viaide1: NVIDIA nForce4 Serial ATA Controller (rev. 0xf3)
viaide1: bus-master DMA support present
viaide1: primary channel wired to native-PCI mode
LTID: Picked IRQ 22 with weight 0
viaide1: using ioapic0 pin 22 (irq 10) for native-PCI interrupt
atabus1 at viaide1 channel 0
viaide1: secondary channel wired to native-PCI mode
atabus2 at viaide1 channel 1
viaide2 at pci0 dev 8 function 0
viaide2: NVIDIA nForce4 Serial ATA Controller (rev. 0xf3)
viaide2: bus-master DMA support present
viaide2: primary channel wired to native-PCI mode
LSI1: Picked IRQ 23 with weight 0
viaide2: using ioapic0 pin 23 (irq 11) for native-PCI interrupt
atabus3 at viaide2 channel 0
viaide2: secondary channel wired to native-PCI mode
atabus4 at viaide2 channel 1
ppb0 at pci0 dev 9 function 0: NVIDIA nForce4 PCI Host Bridge (rev.  
0xa2)
pci1 at ppb0 bus 1
pci1: i/o space, memory space enabled
wm0 at pci1 dev 4 function 0: Intel i82541GI 1000BASE-T Ethernet, rev. 0
LNK1: Picked IRQ 16 with weight 0
wm0: interrupting at ioapic0 pin 16 (irq 11)
wm0: 32-bit 33MHz PCI bus
wm0: 64 word (6 address bits) MicroWire EEPROM
wm0: Ethernet address 00:0e:0c:65:e3:a1
igphy0 at wm0 phy 1: Intel IGP01E1000 Gigabit PHY, rev. 0
igphy0: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT,  
1000baseT-FDX, auto
vga0 at pci1 dev 6 function 0: ATI Technologies Rage XL (rev. 0x27)
wsdisplay0 at vga0 kbdmux 1
wsmux1: connecting to wsdisplay0
wskbd0: connecting to wsdisplay0
fxp0 at pci1 dev 8 function 0: i82550 Ethernet, rev 16
LNK3: Picked IRQ 17 with weight 0
fxp0: interrupting at ioapic0 pin 17 (irq 10)
fxp0: Ethernet address 00:e0:81:30:d6:0a
inphy0 at fxp0 phy 1: i82555 10/100 media interface, rev. 4
inphy0: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, auto
ppb1 at pci0 dev 13 function 0: NVIDIA nForce4 PCIe Host Bridge (rev.  
0xa3)
pci2 at ppb1 bus 2
pci2: i/o space, memory space enabled, rd/line, wr/inv ok
ppb2 at pci0 dev 14 function 0: NVIDIA nForce4 PCIe Host Bridge (rev.  
0xa3)
pci3 at ppb2 bus 3
pci3: i/o space, memory space enabled, rd/line, wr/inv ok
pchb0 at pci0 dev 24 function 0
pchb0: Advanced Micro Devices AMD64 HyperTransport configuration  
(rev. 0x00)
pchb1 at pci0 dev 24 function 1
pchb1: Advanced Micro Devices AMD64 Address Map configuration (rev.  
0x00)
pchb2 at pci0 dev 24 function 2
pchb2: Advanced Micro Devices AMD64 DRAM configuration (rev. 0x00)
pchb3 at pci0 dev 24 function 3
pchb3: Advanced Micro Devices AMD64 Miscellaneous configuration (rev.  
0x00)
pchb4 at pci0 dev 25 function 0
pchb4: Advanced Micro Devices AMD64 HyperTransport configuration  
(rev. 0x00)
pchb5 at pci0 dev 25 function 1
pchb5: Advanced Micro Devices AMD64 Address Map configuration (rev.  
0x00)
pchb6 at pci0 dev 25 function 2
pchb6: Advanced Micro Devices AMD64 DRAM configuration (rev. 0x00)
pchb7 at pci0 dev 25 function 3
pchb7: Advanced Micro Devices AMD64 Miscellaneous configuration (rev.  
0x00)
isa0 at pcib0
lm0 at isa0 port 0x290-0x297: W83627HF
isapnp0 at isa0 port 0x279: ISA Plug 'n Play device support
isapnp0: no ISA Plug 'n Play devices found
pci4 at mainbus0 bus 9
pci4: i/o space, memory space enabled, rd/line, rd/mult, wr/inv ok
pci5 at mainbus0 bus 10
pci5: i/o space, memory space enabled, rd/line, rd/mult, wr/inv ok
mpt0 at pci5 dev 3 function 0: LSI Logic FC929 FC Adapter
mpt0: interrupting at ioapic2 pin 2 (irq 10)
scsibus0 at mpt0: 256 targets, 8 luns per target
mpt1 at pci5 dev 3 function 1: LSI Logic FC929 FC Adapter
mpt1: interrupting at ioapic2 pin 3 (irq 12)
scsibus1 at mpt1: 256 targets, 8 luns per target
bge0 at pci5 dev 9 function 0: Broadcom BCM5704C Dual Gigabit Ethernet
bge0: interrupting at ioapic2 pin 0 (irq 11)
bge0: ASIC BCM5704 A3 (0x2003), Ethernet address 00:e0:81:30:d6:7c
brgphy0 at bge0 phy 1: BCM5704 1000BASE-T media interface, rev. 0
brgphy0: using BCM5704 DSP patch
brgphy0: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT,  
1000baseT-FDX, auto
bge1 at pci5 dev 9 function 1: Broadcom BCM5704C Dual Gigabit Ethernet
bge1: interrupting at ioapic2 pin 1 (irq 10)
bge1: ASIC BCM5704 A3 (0x2003), Ethernet address 00:e0:81:30:d6:7d
brgphy1 at bge1 phy 1: BCM5704 1000BASE-T media interface, rev. 0
brgphy1: using BCM5704 DSP patch
brgphy1: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT,  
1000baseT-FDX, auto
ioapic0: enabling
ioapic1: enabling
ioapic2: enabling
timecounter: Timecounter "clockinterrupt" frequency 100 Hz quality 0
fd0 at fdc0 drive 0: 1.44MB, 80 cyl, 2 head, 18 sec
Kernelized RAIDframe activated
IPsec: Initialized Security Association Processing.
atapibus0 at atabus0: 2 targets
cd0 at atapibus0 drive 0: <HL-DT-STDVD-ROM GDR8164B, , 0L06> cdrom  
removable
scsibus0: waiting 2 seconds for devices to settle...
cd0: 32-bit data port
scsibus1: waiting 2 seconds for devices to settle...
cd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 2 (Ultra/33)
cd0(viaide0:1:0): using PIO mode 4, Ultra-DMA mode 2 (Ultra/33)  
(using DMA)
sd0 at scsibus0 target 0 lun 0: <APPLE, Xserve RAID, 1.26> disk fixed
sd0: 1035 GB, 132522 cyl, 128 head, 128 sec, 512 bytes/sect x  
2171240448 sectors
sd1 at scsibus1 target 0 lun 0: <APPLE, Xserve RAID, 1.26> disk fixed
sd1: 1035 GB, 132522 cyl, 128 head, 128 sec, 512 bytes/sect x  
2171240448 sectors
wd0 at atabus1 drive 0: <WDC WD1600JS-22MHB0>
wd0: drive supports 16-sector PIO transfers, LBA48 addressing
wd0: 149 GB, 310101 cyl, 16 head, 63 sec, 512 bytes/sect x 312581808  
sectors
wd0: 32-bit data port
wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133)
wd0(viaide1:0:0): using PIO mode 4, Ultra-DMA mode 6 (Ultra/133)  
(using DMA)
wd1 at atabus3 drive 0: <WDC WD1600JS-00MHB0>
wd1: drive supports 16-sector PIO transfers, LBA48 addressing
wd1: 149 GB, 310101 cyl, 16 head, 63 sec, 512 bytes/sect x 312581808  
sectors
wd1: 32-bit data port
wd1: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133)
wd1(viaide2:0:0): using PIO mode 4, Ultra-DMA mode 6 (Ultra/133)  
(using DMA)
raid0: RAID Level 1
raid0: Components: /dev/wd0a /dev/wd1a
raid0: Total Sectors: 312581632 (152627 MB)
boot device: raid0
root on raid0a dumps on raid0b
root file system type: ffs
cpu1: CPU 1 running
wsdisplay0: screen 1 added (80x25, vt100 emulation)
wsdisplay0: screen 2 added (80x25, vt100 emulation)
wsdisplay0: screen 3 added (80x25, vt100 emulation)
wsdisplay0: screen 4 added (80x25, vt100 emulation)

-- 
     aew