I'm really interested in that, but I can't figure out how to go about it.
Free apps, you'd assume, would get way more downloads and be a cool and very targeted place to advertise.
I tried starting a thread on a marketing forum about that, but not much response so far.
A simple utility might take a month to develop - say 8-10K development costs, and get 20-30K downloads or more - so 2-3 users per $ spent with ad views every time they open the app.
Well I know apps like UberTwitter (and some others) have ads embedded in the application. I'm just not sure if there is a simple ad network program like there is for web pages (adsense, adbrite, etc) for the BB.