I've a product based around a variety of VIA miniITX boards and I'm 
readying our release of software based on netbsd-4 instead of 3. However, 
I've found that with acpi enabled, one revision of the board doesn't 
notice when usb memory devices are plugged in (the LED on my pendrive 
doesn't light up). A USB mouse works, but plugging in a pen drive kills it 
(device gets detached and won't re-attach). This didn't happen with 
3.1_STABLE (though kernel configs differ between the two, of course).

Any clues on where to look to track this down?

dmesg with acpi:

     The NetBSD Foundation, Inc.  All rights reserved.
Copyright (c) 1982, 1986, 1989, 1991, 1993
     The Regents of the University of California.  All rights reserved.

NetBSD 4.0_RC2 (THINIT) #3: Thu Oct  4 15:42:53 BST 2007
 	root@devel4:/usr/src/sys/arch/i386/compile/THINIT
total memory = 111 MB
rbus: rbus_min_start set to 0x20000000
avail memory = 98 MB
timecounter: Timecounters tick every 10.000 msec
timecounter: Timecounter "i8254" frequency 1193182 Hz quality 100
BIOS32 rev. 0 found at 0xfb380
mainbus0 (root)
cpu0 at mainbus0: (uniprocessor)
cpu0: VIA C3 Nehemiah (686-class), 1002.33 MHz, id 0x698
cpu0: features 381b83f<FPU,VME,DE,PSE,TSC,MSR,SEP,MTRR>
cpu0: features 381b83f<PGE,CMOV,PAT,MMX>
cpu0: features 381b83f<FXSR,SSE>
cpu0: "VIA Nehemiah"
cpu0: I-cache 64 KB 32B/line 2-way, D-cache 64 KB 32B/line 2-way
cpu0: L2 cache 64 KB 32B/line 8-way
cpu0: ITLB 128 4 KB entries 8-way
cpu0: DTLB 128 4 KB entries 8-way
cpu0: 8 page colors
acpi0 at mainbus0: Advanced Configuration and Power Interface
acpi0: using Intel ACPI CA subsystem version 20060217
acpi0: X/RSDT: OemId <CLE266,AWRDACPI,42302e31>, AslId <AWRD,00000000>
acpi0: SCI interrupting at int 9
acpi0: fixed-feature power button present
timecounter: Timecounter "ACPI-Fast" frequency 3579545 Hz quality 1000
ACPI-Fast 24-bit timer
mpacpi: could not get bus number, assuming bus 0
LNKC: ACPI: Found matching pin for 0.13.INTA at func 0: 11
LNKA: ACPI: Found matching pin for 0.16.INTA at func 0: 10
LNKB: ACPI: Found matching pin for 0.16.INTB at func 1: 11
LNKC: ACPI: Found matching pin for 0.16.INTC at func 2: 11
LNKD: ACPI: Found matching pin for 0.16.INTD at func 3: 5
LNKD: BIOS IRQ 5 for 0.16.INTD is invalid
LNKA: ACPI: Found matching pin for 0.17.INTA at func 1: 255
LNKC: ACPI: Found matching pin for 0.17.INTC at func 5: 11
ACPI Object Type 'Processor' (0x0c) at acpi0 not configured
acpibut0 at acpi0 (PNP0C0C): ACPI Power Button
acpibut1 at acpi0 (PNP0C0E): ACPI Sleep Button
PNP0C01 at acpi0 not configured
PNP0A03 at acpi0 not configured
PNP0C02 at acpi0 not configured
PNP0C0F at acpi0 not configured
PNP0C0F at acpi0 not configured
PNP0C0F at acpi0 not configured
PNP0C0F at acpi0 not configured
PNP0C0F at acpi0 not configured
PNP0C0F at acpi0 not configured
PNP0C02 at acpi0 not configured
PNP0000 at acpi0 not configured
PNP0200 at acpi0 not configured
attimer1 at acpi0 (PNP0100): AT Timer
attimer1: io 0x40-0x43 irq 0
PNP0B00 at acpi0 not configured
pcppi1 at acpi0 (PNP0800)
pcppi1: io 0x61
sysbeep0 at pcppi1
npx1 at acpi0 (PNP0C04)
npx1: io 0xf0-0xff irq 13
npx1: reported by CPUID; using exception 16
PNP0700 at acpi0 not configured
com3 at acpi0 (PNP0501-1)
com3: io 0x3f8-0x3ff irq 4
com3: ns16550a, working fifo
com4 at acpi0 (PNP0501-2)
com4: io 0x2f8-0x2ff irq 3
com4: ns16550a, working fifo
lpt3 at acpi0 (PNP0401-1)
lpt3: io 0x378-0x37f,0x778-0x77b irq 7 drq 3
pckbc1 at acpi0 (PNP0F13): aux port
pckbc1: irq 12
pckbc2 at acpi0 (PNP0303): kbd port
pckbc2: io 0x60,0x64 irq 1
PNP0C0B at acpi0 not configured
acpitz0 at acpi0: ACPI Thermal Zone
acpitz0: unable to get polling interval; using default of 30.0s
acpitz0: active cooling level 0: 122.0C
acpitz0: critical 124.0C passive 40.0C
pcppi1: attached to attimer1
pckbd0 at pckbc2 (kbd slot)
pckbc2: using irq 1 for kbd slot
wskbd0 at pckbd0: console keyboard
pms0 at pckbc2 (aux slot)
pckbc2: using irq 12 for aux slot
wsmouse0 at pms0 mux 0
pci0 at mainbus0 bus 0: configuration mode 1
pci0: i/o space, memory space enabled, rd/line, rd/mult, wr/inv ok
pchb0 at pci0 dev 0 function 0
pchb0: vendor 0x1106 product 0x3123 (rev. 0x00)
agp0 at pchb0: aperture at 0xd0000000, size 0x10000000
ppb0 at pci0 dev 1 function 0: vendor 0x1106 product 0xb091 (rev. 0x00)
pci1 at ppb0 bus 1
pci1: i/o space, memory space enabled
vga1 at pci1 dev 0 function 0: vendor 0x1106 product 0x3122 (rev. 0x03)
wsdisplay0 at vga1 kbdmux 1: console (80x25, vt100 emulation), using wskbd0
wsmux1: connecting to wsdisplay0
wsdisplay0: screen 1 added (80x25, vt100 emulation)
rtk0 at pci0 dev 13 function 0: Realtek 8139 10/100BaseTX (rev. 0x10)
rtk0: interrupting at irq 11
rtk0: Ethernet address 00:11:5b:b0:dc:92
rlphy0 at rtk0 phy 7: Realtek internal PHY
rlphy0: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, auto
uhci0 at pci0 dev 16 function 0: vendor 0x1106 product 0x3038 (rev. 0x80)
uhci0: interrupting at irq 10
usb0 at uhci0: USB revision 1.0
uhub0 at usb0
uhub0: vendor 0x1106 UHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub0: 2 ports with 2 removable, self powered
uhci1 at pci0 dev 16 function 1: vendor 0x1106 product 0x3038 (rev. 0x80)
uhci1: interrupting at irq 11
usb1 at uhci1: USB revision 1.0
uhub1 at usb1
uhub1: vendor 0x1106 UHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub1: 2 ports with 2 removable, self powered
uhci2 at pci0 dev 16 function 2: vendor 0x1106 product 0x3038 (rev. 0x80)
uhci2: interrupting at irq 11
usb2 at uhci2: USB revision 1.0
uhub2 at usb2
uhub2: vendor 0x1106 UHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub2: 2 ports with 2 removable, self powered
ehci0 at pci0 dev 16 function 3: vendor 0x1106 product 0x3104 (rev. 0x82)
LNKD: Picked IRQ 9 with weight 0
ehci0: interrupting at irq 9
ehci0: BIOS has given up ownership
ehci0: EHCI version 1.0
ehci0: companion controllers, 2 ports each: uhci0 uhci1 uhci2
usb3 at ehci0: USB revision 2.0
uhub3 at usb3
uhub3: vendor 0x1106 EHCI root hub, class 9/0, rev 2.00/1.00, addr 1
uhub3: 6 ports with 6 removable, self powered
pcib0 at pci0 dev 17 function 0
pcib0: vendor 0x1106 product 0x3177 (rev. 0x00)
viaide0 at pci0 dev 17 function 1
viaide0: VIA Technologies VT8235 ATA133 controller
viaide0: bus-master DMA support present
viaide0: primary channel configured to compatibility mode
viaide0: primary channel interrupting at irq 14
atabus0 at viaide0 channel 0
viaide0: secondary channel configured to compatibility mode
viaide0: secondary channel interrupting at irq 15
atabus1 at viaide0 channel 1
auvia0 at pci0 dev 17 function 5: VIA Technologies VT8235 AC'97 Audio (rev 0x50)
auvia0: interrupting at irq 11
auvia0: ac97: Avance Logic ALC655 codec; no 3D stereo
auvia0: ac97: ext id 9c4<AC97_23,LDAC,SDAC,CDAC,SPDIF>
audio0 at auvia0: full duplex, independent
isa0 at pcib0
isapnp0 at isa0 port 0x279: ISA Plug 'n Play device support
fdc0 at isa0 port 0x3f0-0x3f7 irq 6 drq 2
isapnp0: no ISA Plug 'n Play devices found
timecounter: Timecounter "clockinterrupt" frequency 100 Hz quality 0
md0: internal 5000 KB image area
boot device: rtk0
root on md0a dumps on md0b
root file system type: ffs

-- 
Stephen