If you photograph landscapes, use your camera on a tripod, or shoot a lot of video, the electronic level is one feature that you'll love. I use the electronic level whenever I'm shooting landscape scenes with my tripod. If you ask me, it's probably one of the coolest things on the 7D.
Why is this so cool? In landscape photography, it's not always easy to see the horizon line. Most of the time you'll want your camera to be aligned horizontally with the scene, but when your shot includes mountains, hills, trees, flowers, and so on, you might not be able to figure out how to place your camera. By using the electronic level, not only can you balance your camera horizontally, but if you want your shot to be straight on (with no backward or forward tilt), you can level the shot vertically as well.
There are three different ways to use the electronic level on the Canon 7D: through the viewfinder (see Figure 2), on the LCD monitor, or in conjunction with Live View. I use all three methods, depending on the easiest way to compose my image, and they all work very well.
Figure 2 The electronic level in the viewfinder is helpful for situations when you don't want to use the LCD monitor (or can't use it) to view the scene.