An advantage I can think of to using two (or more) individual monitors over one large one is, if you maximize a window in a dual monitor setup, it stays on the monitor it was on, allowing you to easily maximize another window on the 2nd monitor.

With one big monitor, maximize a window and it covers everything...

Sure there are ways to work around that, but I think it's easier to just maximize...

BTW, 2x24" at work, and a 24" (1920x1200) and a 21" (1600x1200) at home