I'm not running it yet. I don't have any money (for now) to get me such a great 64 bit CPU, so I can't run it.
From what I read, it seems that most programs already run on it. It's quite noticable that's beta though, as there is quite some software that performs worse on the 64bit edition of XP, compared to the 32bit edition (even on the same CPU!).
I'd stick with standard XP (or 64bit Linux :)) for now and wait for the final release to switch to XP 64 bit. Ofcourse, if you want to try the software, just make a dualboot of your system and see how it turns out for you