Here's what you can do to collect more information:

> kernel: page fault trap, code=0
> Stopped in usb0 at _usbd_close_pipe+0x7  movl  0xc(%ebx),%eax

This is probably a null-pointer dereference; to be certain, 

ddb> print $ebx

should show you the value of the %ebx register..

Getting a stack trace at this point will probably be of more use:
ddb> trace

I don't know the usb code very well so i'm not going to try to
speculate on what happened here..

					- Bill