[Bloody Sam Roberts]

Image Your Machine Beforehand

Bingo. Do it religiously once per week if not, more. I use Macrium Reflect and it is awesome. For my Linux, the need isn't so severe but it's just as easy.

[TomServo]

I build images of several installs

1). Base (basically factory)
2). Office Suite
3). Development
4). Daily
5). Games

Each image build incrementally so I can restore at any point. My personal files themselves reside on another drive. So when I restore the "C" Drive, my personal files are untouched.