We had an interesting internal discussion a few weeks ago about the relative merits of dual monitors over big screens. While there were pros and cons on both sides of the argument, it's really down to a question of personal taste whether you prefer one model to the other.

The critical parameter though is the screen real estate - the actual number of pixels available, rather than how they are configured. It doesn't matter whether those pixels are spread across one screen or two. My two main machines - a 24" iMac (1920x1200) and a 17" MacBook Pro (1680x1050, plus an external 20" with 1600x1200) feel equally productive. On one, I have enough pixels to put many windows side by side. On the other, I spread them across both monitors.