It does run on 64-bit (natively), I have it running right now. The linux installer has both 32 and 64 bit binaries inside it, and I must say, it works (almost) flawlessly. There is one issue with it I have, but I think KWin is to blame rather than S2.
It also runs _really_ fast on linux, and it's just a beta. I'd expect it to be much better when it gets released.