Ok for you two with the 5 and 4 monitors, would you want that many if you didn't work on that computer?
I'll be sticking with my dual monitors until the need arises to have way more stuff open and visible at once than I do now. My main monitor is for web browsing, tasks at hand, etc. My secondary monitor handles irc, music, torrent stuff, my VM, and other misc stuff.
I agree with the one anon that talked about 3 monitors exceeding the field of view. I can easily view both of my monitors with a flick of my eyes, three monitor and i know i'd be looking out the corner of my eyes or rotating my head.
http://imageshack.com/a/img844/1008/hre2.pngP.S. before anyone rants at my triple monitor wallpaper I'm posting, I have a tv hooked up but I don't use it as a monitor and thus don't consider it a monitor. It's also on the other side of the room only used for watching stuff.