Currently running Leopard 10.5.1 on my PC. Only issues are the sound card and the $10 PCI wireless card. Tomorrow I will hardwire in from my router and be able to get online with it. The first few times it ran it was fairly unstable (needed reboots every five mins), but after some tweaking (like unplugging ghetto cheap PCI expansion cards) and toying around it seems to be pretty smooth. Just need to get the sound running and I'll be pretty much set. It recognizes the machine as a Mac Pro (2.6c2d OC'd to 3.2, 4gb RAM, WD Raptor, GeForce 7300) and runs very quickly. I'll see how it does in the next week or so with my usual tasks (internet, movies, music, Adobe CS), and if it looks good I'll consider myself XP-free. Glad I bought the parts for the box with a high emphasis on OS X compatibility. Have to get used to the weird OS X mouse action again...very different feel than a PC, even with sensitivity turned up all the way. Is there a hack out there to speed it up more? I'll post some screenies tomorrow.