Does in-app advertising in iOS and other mobile apps actually generate revenue, or is it a worthless business model?

In-app advertising works well for some apps. Pandora, Twitter and Facebook generate hundreds of millions of dollars a year in mobile ad revenue. Unfortunately, not many apps generate the kind of traffic those do to generate large sums of revenue. Most apps today generate revenue between advertising and in app purchases like virtual currency. iAd works for some people and doesn’t for others. It depends on the nature of your app and the kind of ads you want to run in it.