Only thing stopping me from switching to Win 7 RC right now is I'm a bit iffy on my RAID card drivers for 64 bit Win 7. I also ran into some issues with MPC, but that was fixed when I stopped trying to use 64 bit codecs.
I can live with Vista Ultimate for awhile until I see some tested and proven Win 7 drivers for my RAID card. Other than that, I've had 0 issues on my other PCs with Win 7.
I don't pirate OSes either, at least I know it'll work if I buy it. I'll definitely be purchasing a full version of whichever one I get for reformatting and other purposes.