I have Win XP x64 on one of my computers because it was my choice, I cannot tell you whether to or not. You have to make choices yourself. Read the article, and see if this is the way you want to go...
Digital content creators, including 3-D animators, digital artists, and game developers will also welcome the large amounts of memory and performance improvements that make their 64-bit applications run faster and more efficiently.
In response to your second question, unless you work with data intensive programs like what Wombat is saying reagarding 3-d animation or other desinging software (ie autocad, video rendering, etc), X64 can be skipped for now. You should be investing in 64 bit hardware though. Wait for Longhorn to come out in 06.