I've been digging through updates as well and I found this one....

KB941600 - This article describes an update rollup that resolves some
reliability issues in the USB core components in Windows Vista. You will
achieve better reliability in various scenarios by installing this update.

I've removed all of the updates that were installed last week, but I still
can't install the drivers for the USB controllers. Windows just won't let
them install. I still get this error:

The I/O operation has been aborted because of either a thread exit or an
application request.