Running an ATI 5800 Series (5870 maybe?) with
24" Dell on DVI
23" Dell on DVI
23" Dell on display port (monitor has a display port)

It works perfectly but have to unplug the display port screen when I turn on the computer or the ATI card's fan goes nuts and doesn't get a display on any of them. I didn't get any usb cable thingo to get extra power with my card. Been running with three screens off it for some time now.