if I have a running NetBSD-current and insert this memory stick, I get:

umass0 at uhub0 port 1 configuration 1 interface 0
umass0: BUFFALO Petit Drive, rev 1.10/1.00, addr 2
umass0: using SCSI over Bulk-Only

but I never get the SCSI disk device binding.

If I insert the device and reboot, *then* it works fine:

umass0 at uhub0 port 1 configuration 1 interface 0
umass0: BUFFALO Petit Drive, rev 1.10/1.00, addr 2
umass0: using SCSI over Bulk-Only
scsibus0 at umass0: 2 targets, 1 lun per target
scsibus0: waiting 2 seconds for devices to settle...
sd0 at scsibus0 target 1 lun 0: <BUFFALO, Petit Drive, 1.06> disk removable
sd0: mode sense (5) returned nonsense; using fictitious geometry
sd0: 64000 KB, 62 cyl, 64 head, 32 sec, 512 bytes/sect x 128000 sectors

And subsequently, for that boot, I can insert/remove to my hearts content.

Is there some 'trick' to make a USB device be recognized without reboot on the
SCSI binding? Is this because a scsi emulation layer or the scsibus0 isn't
initialized in the kernel unless its got an attached device at boot time? 

I have scsibus* at umass? in my kernel config.

Dell L400 laptop, normal wd/atapi disks.

-George