I had problems getting Xgl working on my box at work (ATI) but sure enough my dual 733 at home with an Nvidia works like a champ. This forum thread got me going.
This is the alt-tab behavior. F12 also behaves like exposse. All of these effects definitely give the experience a lot more polish. I can't wait until all this stuff is mainstream and enabled by default (Dapper + 1 I hope).