For the past year we have been hearing a lot more of 64-bit as the next big step in personal computing. Put in simple terms, going 64-bit would double the amount of data a CPU can process per clock cycle.
It's true a 64-bit desktop computer won't make your word processing program run faster (sorry, you're the bottleneck in that equation). But a 64-bit chip has the power to dramatically improve the performance of your more demanding applications, such as audio and video encoding, complex engineering programs like CAD, and--of course--games. And in the long term, 64-bit computing will give programmers much more power to play with, and could revolutionize what desktop software can do.
Intel has been offering Itaniums to the server and workstation markets for some time now, we all know AMD Opterons are available already & AMD's next mainstream piece, the Athlon 64 will arrive later this year. PC World has an article explaining short and long-term advantages we are most likely to see with the arrival of the next generation of desktop computers.