I just bought a new 27" Quadcore iMac. It's a really fast machine until I try PlayOnMac.
The GUI seems to get stuck for a secound than it works for e few secound than it stops for a secound and so on.
This is annoying, but after installing WinRar the program seems to work without problems, only the POM-GUI itself has very bad performance.
Now I tried Fallout: New Vegas. The installation was very annoying again, but the game seems to run.
On the beginning inside the house everything seems to be ok, but after going outside the game is unplayable slow, even with graphics set to low. I think the Radeon 5750 should do it!?