This is a terrific example of how to use Push Notifications for mobile Apps. Below is a screen shot from Fandango's iPhone App - from which we bought tickets to see The Lorax. Fandango obviously knows when the movie is - and when it ends. Almost immediately after it ended, I got the following push notification. Obviously highly relevant - and because there is no better time to deliver it, I don't find it spammy or unwelcome.
Very smart. Very simple. But not commonly done!