The winsxs folder bloats as you uninstall apps! This is counter-intuitive to gaining hard drive space huh? Within a week of running Windows 7 many people report a windows/winsxs folder to be 5 Gigs and as much as 10 to 12 Gigs.
What is the winsxs folder? A complicated mess that microsoft made, like the registry but even more of a black box space hog.
It contains manifests, dll backups, service pack backups, libraries for executables and other serious sounding junk. So many MS guys advise not to touch it that even I…windows modder and tinkerer from the win3.1 days have not dared delete any of the jillion little folders which turns out to the the bulk of my 5.5 Gigs of use.
My advice is to image your hard drive fairly often and when you want to uninstall stuff, go back to your image instead, of course after you’ve made sure you’ve copied your docs and bookmarks etc.