I would let Win XP 64 stay on the market for a while, many manufactures have to upgrade their drivers and software before they will work with Win XP 64. Once the updated software becomes available then I would consider switching.
I couldn't have stated it better myself. I honestly think that win XP-64 first comes out, it will bring a decrease in performance in 32 bit apps, especially games, until people like ATI and Nvidia get good 64-bit drivers out, or game manufacturers recompile the code in 64-bit.
