You'll also want to avoid using the migration assistant if moving over from a PowerPC Mac. A user on the Apple forums had all manner of problems with his 3rd drive bay, moved the hard drives around, it still stuck in bay 3, but then started affecting other drive bays. Turns out the migration was about 5 machines old, all of them before that PPC.
Like MacGeek said though, the Pros been very bug free which is great to hear. There was one DOA MacPro reported on Macintouch, they tried re-seating the RAM riser cards (which worked for Macintouch' DOA MacPro) and that was a no go. So he had to send it back to Apple.