Do multiple screens help you to mentally divide tasks? Are they worse ergonomically than a single ultra-large screen? What do you prefer?
Once upon a time, I was partial to multiple screens. It's one of the things that got me into Macs: Back then, they were the only computers that could handle multiple screens as a single desktop, seamlessly. I would have Photoshop on full screen on the main one, use the right one for palettes, and the left one for other programs, like mail.
With time, however, I found it wasn't that convenient. The screen with the palettes, even while calibrated, will shift in color compared to the central screen (or viceversa). And I found myself looking to the sides too much, so at the end everything ended up in the main display.
After a while, I got a really large monitor and got rid of the rest. Years later, when I got the iMac 24 and Apple introduced Exposé, I just couldn't give a damn about multiple screens anymore. Now, all I want is an iMac with a 30-inch, 200dpi screen, and Exposé.
There's only one way I would get another screen: I want one of those tiny 7-inch portrait USB displays for my chat client.
What about you? Are you a multiple screen or a huge screen fan?