When I have a beta or a RC of some Microsoft product, I'll install it directly on my primary machine (which is a notebook), which I usually use for software development. I do that because I usually really want to use the beta product in the most appropriate
way. If I would have installed it into a test machine, I would probably skip (because of my comodity) a lot of tests (that otherwise I will do on the primary machine as "work" and not "tests").
Of cource, from time to time this behaviour that many don't understand in me leads me to reinstallations from scratch, but they are not that painful as one may think.
I have Ghost packaged backupt for the OS (Windows XP OEM) and then I only install software that I need: Visual C# .NET. That's the only thing I really need beside the OS. Of course, I also restore My Documents, Visual Studio Projects, etc. from the latest incremental
backup (I usually create 1 backup CD with such data) every two weeks (sometimes sooner, sometimes later, depending on my free time). The backups are not always exactely incremental as I don't use a backup tool (since Windows's Backup does not allow me to backup
directly to a blank CD), but instead I copy the new projects, files, etc. manually to the CD. I admit, it may happen one day that I forget to place a file to the backup folder on a CD and I will probably lose that file, but hey, that's life. However, never
happened to me yet... hehehe...
So, as a conclusion, I think that the paradox is solved for me: I install everything on my primary machine, until it goes down the drain and then reinstall... after Windows XP the time between reinstalls is a lot larger: about 6-12 months. It's good enough