I made a very simple iOS gym log app for my own needs and decided to sell it in the App Store. I think I've generated almost $5k in revenue. So, not a 'business', but it certainly paid for my developer account! :)
Iroically, the app isn't truly native, but was built in jQTouch. When I get around to it, I'm planning to finish a native version, which I think it desperately needs to be.