So far, so good
I've been running the Release Candidate on my new pc for about six weeks now (TRS2004 and 2009) and I'm quite pleased with it.
Note there's no 'direct' upgrade from XP. You will need to buy the full version and totally install from scratch, reinstalling your programs etc. I usually don't recommend an upgrade to a new OS, due to the rapid development of new hardware. It's usually better to buy or build a new pc.
The system requirements for 7 are basically the same for Vista - steep! I would recommend two gigs of RAM minimum, 4 preferred.
Ferngren is correct regarding the XP mode; however, you must have a cpu that supports it (and a licensed copy of XP).
Darrel