This one’s for all you Macbook and Magic Trackpad users; you know who you are. Mac OS X comes with Mission Control, a way to see all the open applications running on your Mac. Typically, you can hit the F3 key to bring up Mission Control and see what’s what on your Mac.
Similarly, you can either click on any Desktop Space across the top of Mission Control, or hit Command-Arrow (right or left) to switch to different Desktop Spaces on your Mac. This makes it easy to visually keep things separate. Some folks keep their web browser in one Desktop Space, and their word processing app in another, switching back and forth as they need the respective apps.
If you’re using a trackpad to access your Mac OS X laptop, or you’re using a magic trackpad connected to your Mac desktop, however, there are a couple of cool trackpad gestures you can use to do the same thing.