I run my application on the left screen, my editor (two files side-by-side) on the main screen, and a bunch of misc windows on the right screen (watches, stack, documentation, etc). I like it.
I think I may have made the wrong choice though. This setup is so wide that turning my head from one screen to another has become a usability issue. The aspect ratio of the whole system doesn't match the aspect ratio of my eyes, and I think that's less than ideal.
So, the next time I upgrade my display I will probably opt for one huge screen rather than multiple merely-large screens.
That said, I'm not really complaining... I really like the setup I have. I've been using multiple monitors since that meant an 80x25 monochrome display on an ISA MDA card, and in general I think they're great. Debugging on a single monitor has always been an annoyance in the past. But from where I sit, the grass looks just a little greener on the Apple Cinema side.