64 bit is one thing that most desktop applications can take their time about adopting. True it allows very large gobs or RAM to be addressed without paging to disk, which is very nice for server applications running hundreds of threads: and it makes the OS more secure, because a lot of the exploits that hackers use to gain control of your machine will just never work on 64 bit Intel: but the speed gains of things like the increased register stack in Intel 64 is offset by the fact that twice the data has to be pushed around and stored. Photoshop likes large gobs of RAM, so 64 bit hits a sweet spot, and I expect the next version to be 64 bit, just like Aperture and Lightroom. However, one cannot infer from that, that what is good for Photoshop is good for everything.
XPress already uses the vector processors (Altivec and SSE2) on your circuitboard, on the Mac uses the GPU via Quartz, and in the future will most likely make good use of all those cores in your brand new machine.
Meantime, to make everything run faster, maybe think about a solid state drive and plenty of high quality of RAM: that's going to help productivity a lot more than 64 bit for everything except image and video crunchers.