Performance-wise, x64 seems pretty overhyped
|In general, though, the situation with 64-bit applications and 32-bit applications on Vista 64 isn't mature yet. While a user running large data sets will almost certainly see improved performance, users with less demanding needs may actually see reduced performance. As always, check with the software supplier, and see if you can run a few tests of your own first.
The bottom line: 64-bit Vista is certainly viable from a performance perspective, but still has a ways to go. Now if we can get all the apps developers to think in 64-bit mode, maybe we'll get better performance all around. But don't forget to stock up on memory.