If you happen to visit Apple's web site, you'll notice that they have a ticker actively counting down to the 10 billion mark for app downloads from its App Stores. Although there is still some time before it finally reaches the mark, Apple is planning to give away a whooping $10,000 gift card to whomever happens to be the one lucky person to perfectly time the mark of hitting the 10 billion mark. That's a pretty substantial prize when you're only required to download an app of some sort from their App Stores.
It just goes to show how the market surrounding apps is not only competitive, but also a profitable one as evidence by the top notch paid ones out there such as Angry Birds.
source: Apple via MobileCrunch