Guys, what you are doing to your computers? I have laptop running for 4 years now, workstation for 1 year since the release of windows x64 and work pc for 3 years. I never had to reinstall it.
Oh and by the way, there registry can not slow down your pc, because it is only few megabytes in size. And even with a lot of software installed and uninstalled it increases only by few kilobytes. It's a myth.