We have an external USB2 disk drive that we can plug into some Dell Optiplex 
GX260's and access quite happily:

uhci0 at pci0 dev 29 function 0: Intel 82801DB/DBM USB UHCI Controller #1 
(rev. 0x01)
uhci0: interrupting at irq 11
uhci0: setup of reserve of size 262144 successful; p 017e8000 v 0xda960000
usb0 at uhci0: USB revision 1.0
uhub0 at usb0
uhub0: Intel 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 29 function 1: Intel 82801DB/DBM USB UHCI Controller #2 
(rev. 0x01)
uhci1: interrupting at irq 10
uhci1: setup of reserve of size 262144 successful; p 0182e000 v 0xda9a2000
usb1 at uhci1: USB revision 1.0
uhub1 at usb1
uhub1: Intel 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 29 function 2: Intel 82801DB/DBM USB UHCI Controller #3 
(rev. 0x01)
uhci2: interrupting at irq 9
uhci2: setup of reserve of size 262144 successful; p 01873000 v 0xda9e7000
usb2 at uhci2: USB revision 1.0
uhub2 at usb2
uhub2: Intel 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 29 function 7: Intel 82801DB/DBM USB EHCI Controller (rev. 
0x01)
ehci0: interrupting at irq 3
ehci0: EHCI version 1.0
ehci0: companion controllers, 2 ports each: uhci0 uhci1 uhci2
ehci0: setup of reserve of size 262144 successful; p 018b8000 v 0xdaa2d000
usb3 at ehci0: USB revision 2.0
uhub3 at usb3
uhub3: Intel EHCI root hub, class 9/0, rev 2.00/1.00, addr 1
uhub3: single transaction translator
uhub3: 6 ports with 6 removable, self powered
 [...]
uhidev0 at uhub0 port 2 configuration 1 interface 0
uhidev0: Logitech USB Optical Mouse, rev 1.10/21.10, addr 2, iclass 3/1
ums0 at uhidev0: 3 buttons and Z dir.
wsmouse0 at ums0 mux 0
 [...]
umass0 at uhub3 port 3 configuration 1 interface 0
umass0: Genesys Logic USB TO IDE, rev 2.00/0.02, addr 2
umass0: using SCSI over Bulk-Only
scsibus0 at umass0: 2 targets, 1 lun per target
sd0 at scsibus0 target 0 lun 0: <ST32122A, , 0811> disk fixed
sd0: fabricating a geometry
sd0: 2014 MB, 2014 cyl, 64 head, 32 sec, 512 bytes/sect x 4124736 sectors
sd0: fabricating a geometry


BUT if we try to plug the same external disk into a new Optiplex GX280 we see 
nothing:

uhci0 at pci0 dev 29 function 0: Intel 82801FB/FR USB UHCI Controller #0 (rev. 
0x03)
uhci0: interrupting at irq 9
uhci0: setup of reserve of size 262144 successful; p 01fb8000 v 0xdb451000
usb0 at uhci0: USB revision 1.0
uhub0 at usb0
uhub0: Intel 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 29 function 1: Intel 82801FB/FR USB UHCI Controller #1 (rev. 
0x03)
uhci1: interrupting at irq 5
uhci1: setup of reserve of size 262144 successful; p 01ffe000 v 0xdb494000
usb1 at uhci1: USB revision 1.0
uhub1 at usb1
uhub1: Intel 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 29 function 2: Intel 82801FB/FR USB UHCI Controller #2 (rev. 
0x03)
uhci2: interrupting at irq 3
uhci2: setup of reserve of size 262144 successful; p 02043000 v 0xdb4d9000
usb2 at uhci2: USB revision 1.0
uhub2 at usb2
uhub2: Intel UHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub2: 2 ports with 2 removable, self powered
uhci3 at pci0 dev 29 function 3: Intel 82801FB/FR USB UHCI Controller #3 (rev. 
0x03)
uhci3: interrupting at irq 10
uhci3: setup of reserve of size 262144 successful; p 02088000 v 0xdb51e000
usb3 at uhci3: USB revision 1.0
uhub3 at usb3
uhub3: Intel UHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub3: 2 ports with 2 removable, self powered
ehci0 at pci0 dev 29 function 7: Intel 82801FB/FR USB EHCI Controller (rev. 
0x03)
ehci0: interrupting at irq 9
ehci0: EHCI version 1.0
ehci0: companion controllers, 2 ports each: uhci0 uhci1 uhci2 uhci3
ehci0: setup of reserve of size 262144 successful; p 020cd000 v 0xdb564000
usb4 at ehci0: USB revision 2.0
uhub4 at usb4
uhub4: Intel EHCI root hub, class 9/0, rev 2.00/1.00, addr 1
uhub4: single transaction translator
uhub4: 8 ports with 8 removable, self powered
 [...]
hub5 at uhub3 port 1
uhub5: Dell Dell USB Keyboard Hub, class 9/0, rev 1.10/2.00, addr 2
uhub5: 3 ports with 2 removable, bus powered
uhidev0 at uhub0 port 1 configuration 1 interface 0
uhidev0: Logitech Optical USB Mouse, rev 2.00/3.40, addr 2, iclass 3/1
ums0 at uhidev0: 3 buttons and Z dir.
wsmouse0 at ums0 mux 0
uhidev1 at uhub5 port 1 configuration 1 interface 0
uhidev1: Dell Dell USB Keyboard Hub, rev 1.10/2.00, addr 3, iclass 3/1
ukbd0 at uhidev1
 [...]
wskbd1 at ukbd0 mux 1
wskbd1: connecting to wsdisplay0
uhidev2 at uhub5 port 1 configuration 1 interface 1
uhidev2: Dell Dell USB Keyboard Hub, rev 1.10/2.00, addr 3, iclass 3/0
uhidev2: 3 report ids
uhid0 at uhidev2 reportid 1: input=1, output=0, feature=0
uhid1 at uhidev2 reportid 2: input=1, output=0, feature=0
uhid2 at uhidev2 reportid 3: input=3, output=1, feature=1
 [...]


Both systems are running identical kernels and userlands and are -current from 
around November and its not just this external drive, the 280's seem a lot 
more finicky with usb devices in general.  Any ideas whats going on here?  
How to make the 280's work?

cheers
mark