I recently stumbled upon a shortcut for switching cameras in the viewport. Normally, you go up to the
Panels heading on the
Panel Menu Bar and chose the camera that you want from the drop down menu. You can also use the marking menu to select the default start-up cameras (
persp, top, front, side), but if you wanted to use this to select other cameras, you would need to setup a custom marking menu and connect it to a MEL or Python script that queries the cameras in your scene... a tutorial for another day.
In any case, the new trick that I found is pretty cool. If you
middle mouse drag a camera from the outliner into the 3D viewport, the view will switch to that camera. Simple as that.

If you have a lot of cameras in your scene, and you're switching around a lot while animating, it can be a pretty nice shortcut.