I must also add that, in many situations, 64-bit is not only unnecessary; it's undesirable due to driver support (currently) not being as strong as in 32-bit. I have several pieces of music recording hardware that won't work with 64-bit because there are no drivers (thank you Line 6 :|)
64-bit does have a lot of pluses, and it's the future, no doubt. The maximum amount of RAM available for the OS increases dramatically, as well as the maximum amount of memory that a process can be assigned.
However, unless you desperately need to use 4GB of RAM or more, I strongly suggest you stick with 32-bit.