We have 42 apps in the App Store, 60 in the wild.
Our success in the App Store is all over the map. Our Enterprise Apps, the 18 not in the store, are our most successful revenue generators. Why? Because we charged the customer for development and in some cases also get maintenance payments. Just like real software...
In the App Store, we have both paid and ad supported apps. Some sell very well, though we are not in the top 50 in an category.
Some do very poorly, and we are working on ways to improve their return. You do have to advertise and get the word out. This takes cash. Our ad budget would scare you I'm sure...
Some have in app purchases that generate the bulk of their revenue.
None of the ad supported apps has been worthwhile, again you need to get a million downloads to get enough people clicking through ads to generate any interesting return.
There are plenty of opportunities to make money for well written apps. You need to understand your demographic and do what appeals to them.
Good luck.
-t