BadOmen, experience is the major reason why we have not transitioned to either XP64 or Vista64, but as to the ?general state of 64bit OS? thing are fine, for most new hardware & apps.
By fine I mean they work, whether or not they have been optimised so that they are multi-threaded & can efficiently use current quad-core CPUs or have been written natively in 64bit, is an entirely different story, however some 3D apps are, but little else.
There is nothing special about Photoshop CS3 that would make it run better in a 64bit environment, it is not coded in 64bit & it is not truly multi-threaded, however it has begun to take advantage of your graphics card, which is a big step in the right direction.
If you don?t have legacy 3rd party hardware to support & your doing a fresh build, then I concur with Winterpool & Sylvanas, Vista64 is definitely the way to go & if you?re into graphics don?t be shy with the RAM or your graphics card.
Regards, Dizz