I actually got that demo but I couldn't install it on my comp because the 64-bit OS won't recognize the SATA drivers for my hard drives. I'll wait until microsoft comes out with a definate 64bit OS that you can buy from a place like staples.
If they're giving it out free, it probably means it's full of bugs that they want their customers (ie. guinea pigs) to report. If I had a 64-bit, I'd definitely try it, but I don't. On the other hand, if I got a 64-bit system now it would probably be a G5, so I wouldn't be able to try it anyway. Not that I would care so much (mmm....Panther...)