Cool Tools: 30″ Cinema Display: A pretty good explanation of why you need a 30” monitor.
Within a few days of using a large screen I began to experience a much more significant effect, though: when more of the things I needed to look at were already in view, the amount of time spent on visual context switches went down. Having more documents in view not only reduces the time consumed by the switch, but also the “recovery time” needed to remember what I was doing.
I have a 24” Dell monitor, and I don’t think I could go back. I also don’t think I would go back to two smaller screens either. I used to think managing two screens independently would be better because you could maximize one app to each, but having a 24” screen has really eliminated my need to desire to maximize anyway.