Are you a Magic Trackpad or MacBook user? Once the Application Switcher is on your screen (you must keep the Command key down), you can use your trackpad to navigate and select something from it.
The most obvious way is to use your finger to move the cursor to select an application and click it. A less obvious, but quicker way to navigate a long Application Switcher bar is to use a two-finger swipe when it's open: applications are quickly highlighted in turn, and the selection wraps when you reach either end of the bar. Pressing Return moves you to the selected application, while your cursor remains in the position where it started, instead of, perhaps, at the far edge of your screen.
If you're working on a late-model Mac, you have an additional, handy option: a 4-finger horizontal swipe opens the Application Switcher and highlights the previous application as the default. With the bar open, you can use the other swipe gestures to select and move to an application. A tap or a press of Return switches you to that application; a second four-finger swipe, or a press of Esc closes the Switcher. Turn on this option using the Trackpad pane in System Preferences.
Long-time Mac writer Sharon Zardetto remembers the thrill of the Mac's first Switcher program, by Andy Hertzfeld.