If you use more than a couple full-screen apps in Lion or Mountain Lion, you can rearrange them in Mission Control to make switching between them more convenient. Simply trigger Mission Control, then at the top of your display, click and drag your full-screen apps to the left or right of each other, just like rearranging app icons in your Dock.
To invoke Mission Control, you can use either a three- or four-finger swipe up on your trackpad or, on newer Macs, the F3 Mission Control key. To switch between full-screen apps, it’s a three- or four-finger swipe to the left and right. Both of those gestures can be configured in System Preferences > Trackpad.