I just fixed 3 major bugs in ehci, and 1 in ohci.  If you were having problems 
with either of these, please try again with ehci.c 1.58 and ohci.c 1.147 or 
later.

I'm now able to run two USB2 disks simultaneously off the same controller, 
getting an aggregate of 210Mb/s.  There's probably some more tuning possible.