You will probably have a headache with triple 28"
I doubt it; the select few with triple 30" monitors at 7680x1600 seem to like it quite a bit.
Here's Maxishine, that crazy Aussie, playing Crysis Warhead across three 30 inchers at 7680x1600:
http://www.youtube.com/watch?v=RPCJh8tYri0
For that, you really need two 5970s. Three 28" monitors won't be a slouch, but they won't require the absolute top of the line, since WUXGA (1920x1200) is about half the resolution of the 30" monitors.
EDIT: Also, there's another thread somewhere on the forums about creating your own multi-monitor case to shrink the bezels. I don't know if you're interested in that much work, though.
http://www.mikevanelst.com/monitorproject/