On my desk I use 3 monitors: 2 big 27" screens and my laptop screen. While it is tempting to put all your live Twitter, Facebook, and email feeds blinking on the left and right screen, I keep them blank most of the time (well, that is a good use of the monitor) to minimise distraction.
I use them when I need a little extra desk space for a slide I am working on: a previous version of a presentation with comments, comments in email, the Finder window with images, a spreadsheet to copy data from. As soon as I am done with that, I close the window with only the wallpaper left.
In a recent software update, Apple has added a new feature: right-click an icon in the dock, click options, and you can now select the default screen the application will open. I set the default for all my smaller utilities (1Password, Evernote, the Finder window) to the small laptop screen.
Art: Gustave Caillebotte, Young man at his window, 1875