When I use Emacs in GUI mode, I set it up to have two 80 column windows side by side. It's extremely convention when you need to look at one section of the code while writing another. For instance, you can have the spec file side by side with the code when doing TDD. Sometimes I want to swap the windows. This kind of functionality does not come built in with emacs. I found the swap-windows function that I use in Steve Yegge's .emacs file.