Most techie guys around here most likely don't mind installing a new OS and I imagine that most have a few extra HDD's laying around. Swap out HDD's and then do a fresh install of WIn7. From what I've read, the RC doesn't expire until mid next year. That gives you a whopping 6-9 mos to try it out. By then, you'll/we'll be wanting to do a fresh install.
Of course, this is JMO.
I've been running Win7 for a few months now and I believe it's by far the best Windows OS to date! I thought I would try and run XP forever (I skipped Vista) but when I built my new computer I thought I'd give the RC 64bit version a go. It's very fast and has crashed like... never! Everything I used before is compatible the only problem I had was getting my printer to share on my Vista laptop. But I think that's totally a Vista issue (we JUST got the laptop). Luckly it's getting a free Win7 upgrade in October.
I don't know if I would recommend installing the RC version because yes- you are going to have to reinstall a new copy of windows and that is a pain in the a**. I would simply recommend buying it when it comes out and be done with it. I am glad I have tried the RC version because I am looking forward to BUYING it!