Really, the more monitors the better as far as I'm concerned. For my home desktop I just have an ultra widescreen and it's basically fine for most stuff as I functionally treat it like two monitors when doing anything outside of a game - I'd still love a second though, especially for while gaming as I miss having a wiki or whatever up in view.
For work we provide everyone with a laptop and two monitors, so that's three screens. Even the least technical of our staff love it and would hate to go back to having less screens. It's so helpful having multiple websites/spreadsheets/whatever open at once when working on anything involving comparing information.