My primary computer at work is a laptop with 17" screen, so that and a second monitor (I think 19" - never measured it) is what I use. There's no way I could function with just a single monitor. I also have a second computer at my desk with one monitor I use quite often, and with it I have three monitors at my disposal. I used to use Synergy to share my clipboard between the computers which was NICE, but it's too buggy so I just save to a shared and reopen on the other computer now in the rare occasion I have to copy between systems.