Every once in awhile you see something that is just so epic, it isn't able to be contained in a single image. You could be at a concert and want to capture the stage and the crowd with one shot or you could be walking around New York and see the most massive alien spaceship that you've ever seen (wait, that was Independence Day). These moments need something better than a normal picture.
If you're in this situation, You Gotta See This! is the app for you. Instead of just taking a simple panoramic shot, the app uses the iPhone 4's gyroscope to determine the proximity of the shots to the original, creating a single large picture that can be extremely wide and tall at the same time. Because of the sensitivity of the gyro, it also lets you take pictures that are diagonal, letting you blend pictures together from any angle that you want.
Check out the tutorial video on the uses of the app, as well as some examples of what the app can do, here. Pick it up in the App Store today for "less than a tall Cappuccino at your local cafe" (reason #4 for buying the app, according to the iTunes page).