I've tried it on both my Athlon 64 X2 4600 (2GB RAM, GeForce 6800 256 MB) desktop (running Windows X64) and my Turion MT-40 laptop (2GB RAM, WinXP Pro, Radeon X1600 256 MB) ...so far, I've been pleased with P7 - I haven't noticed a huge speed boost, but it has been able to render some scenes P6 would choke on without a problem and  without needing to decrease the bucket size or lower the quality.

From what I can tell, the multi thread feature is a real mixed blessing...this is not a true multiprocessor renderer (like Carrara), it seems more designed to help with the setup and memory workload rather then the actual rendering...in simple scenes, in fact, having it multithreaded actually seems to slow things down. I'm no expert at this stuff, but I would image the real advantage to enabling multiple threads would be to get around the memory limitation to a single thread in Windows for very complex scenes.