I daily work on 32 bit and, Xp and Vista, and on a 64 bit Vista system. On
routine work no difference that would justify moving to a Bit system. The
real difference is when you have to handle heavy workloads/files. Handling
2-3Gb files on a good 64 Bit system is as smooth as handling 200 Mb on a 32
Bit one, that's one of the reasons 64 Bit systems are used in the graphics
market.
It all depends what you are going to use it for, it's not worth it if you
are not going to use the full potential of a 64 Bit system. And of course
you would have a software and driver compatibility problem to consider
first.
AndyB