I use it, and it's faster though it depends on what kind of scenes you do. You'll see more benefit if you regularly do heavy scenes that run out of RAM. In those, ppro will use all the RAM you can throw at it and render much faster. In smaller scenes you will see a lesser improvement.

Also note that while the rendering in ppro is 64 bits, the rest of it isn't. This means that there is still a practical limit to how complex a scene you can work with. If it takes more then 3-4 GB RAM (unlikely, but it can happen) then you will run into the same problems as 32 bits.

As for XP64 compatibility issues, there are virtually none now except for perhaps printer drivers for some companies/older printers. If you're worried about this, wait a few months and get win7 64 instead.