I am running am Intel i7-2600K with a couple of ATI Radeon HD 5400 series cards, and four Samsung SynMaster 2253BW's. I tried a number of distros, tried ever trick Google fed me, and never managed to find a way to get all four monitors going properly. The closest I ever got was to have the screens for each card mirrored. I gave up and ran Windows 7.
So, if anyone has had any luck, I would love to know as well. While I hate to admit that W7 has run flawlessly, I would still rather be using *nix on this machine....