Microsoft officially released two new fixes "performance" and "compatibility" packs. They are not available through Windows Update yet, only through the Support site. (KB938979 & KB938194)
KB 938979, aka the "performance and reliability" update addresses poor memory management performance (I want my memory back!). Also fixed is the nasty problem installing printers when User Account Control is disabled as well as the ever-so-annoying networking flaw that would strike TCP/IP dead after a computer wakes from hibernation. The best part is a fix for the "estimated time remaining" taking FOREVER to calculate when transfering large files.
KB 938194, also known as the "compatibility and reliability" update, should probably be called the "now you can play games with your computer" update. It purports to address a handful of gaming-related problems, including compatibility issues with NVIDIA's G80 series of cards. The lame printer spooling bug that was afflicting many of you has also been addressed.
And as always, read the KB entries and Vista forums before installing just to see what to expect.