KB 938371, the slayer of mice
WIndows Update installled 938371 onto my Vista box, taking out my Logitech USB mouse. After much torment and fermentation, the following work around brought my mouse back to life.
* Go to device manager -> HID-devices -> Unknown Device and search for drivers.
* When prompted for how to search for driver software, select "Browse my computer for driver software"
* Enter "C:\windows\winsxs" for the driver location and press the "Next" button.
* If you get a popup saying "this is an unsigned driver...", just allow Windows to install the driver.
At this point, Windows should select the appropriate driver and your mouse will start working again.