I've recently ordered 3x 21.5" monitors for developing with. It'll be interesting to see how Precise / Unity handles that setup. I have either Nvidia Optimus on my T420s Thinkpad or ATI 5970s to test with.
I've got that setup with a 5970 eyefinity 6 card. The monitors are in portrait mode so it's like one big 3240x1920 surface.
Developing what with? I got hacked off with issues with multiple monitors - and in the end - just went back to one monitor with multiple work spaces. I figured in the end they were nothing but a distraction.