The main benefit is that you can address > 4 GB of RAM, which means that if you have 4+ GB installed you don't lose any of it to legacy crap that steals the addresses. The downside is that device driver and other compatability for 64-bit can be spotty. I'm personally happy with what I get from the 64-bit nVidia drivers, but I do have some lingering issues with multiple GPUs that might go away if I reverted back to Vista x32.