I used to swear by multiple monitors, but work took back my secondary monitor then I "adopted" a 30" HP that wasn't being used, and am now 100% converted to using a single large monitor and loving it. The fact that I can scatter differently sized windows around my view area depending on what size they require, and how much of my attention they need, has definitely increased my productivity. I also like that i'm not always turning my head left and right as much.
