Here's an interesting report from Juniper Research. According to their work, mobile app revenues will reportedly grow from the current US $6 billion to a whopping $11 billion by 2015. And the majority of that revenue will come not from the standard download fee, but instead from in-app purchases, according to Juniper. The firm claims that in-app purchase revenue will top one-off download fees by 2013. That seems hard to believe, given my current anecdotal usage, but there's no question that in-app purchases are growing by leaps and bounds as a form of sizable revenue for app developers.
Jupiter's report also says that the biggest problem facing mobile app growth is just plain discovery -- with so many apps out there, it's hard for users to find new apps that they like, so what you tend to see is clumps of apps getting popular rather than users going out and finding their own favorites. Services like OpenFeint and Game Center have certainly helped to share information about new apps, and of course sites like ours try to spotlight as many apps as we can. But with a store full of hundreds of thousands of apps in it, it's tough to let more than a few hundred really shine. Maybe as we move forward, developers and Apple will come up with better solutions to help do that.