One of Lion’s hallmark new features was its introduction of Multi-Touch gestures. By now, you may well have learned most of them. But there’s one you probably don’t know about because it’s hidden.
If you use the four-finger swipe to move from one desktop to another, or to a full-screen application or the Dashboard, you can quickly go to the previous workspace or application by executing a four-finger double-tap.
To enable that gesture, open Terminal (in /Applications/Utilities) and type this:
defaults write com.apple.dock double-tap-jump-back -bool TRUE;killall Dock
The first part of the command enables the double-tap; the second (after the semicolon) puts it into effect. To test your new gesture, swipe to the right with four fingers to reveal the Dashboard, and then double-tap with four fingers to come right back to the desktop.