For about three months I’ve been using 64 on an 8 core with 20GB of ram connected to a Proavio 8 15k drive raid array/ SAS with no problems.
I use a lot of weird little programs and have yet to have an xp64 problem which surprised me. My friends had been using it (mainly 3ds max guys) and convinced me to try it.
So far, so good.
Now, for home, I’m looking at an 8 core 3.2 Mac Pro, 16GB ram, with a calDigit raid… still researching that.