While some of this stuff was outlined at the release of iPhone OS 3, Businessweek conjures up some other possibilities for App sharing:
One example of P2P connectivity will be available in the new iPhone 3.0 software, due this summer. Users will be able to play multiplayer games with one another using Bluetooth connectivity, rather than needing to be on a carrier’s network. A player’s phone will automatically detect nearby iPhones and iPod touches that run the same app and send them an invitation to join the game. Initially, the feature will work only when both parties already have a particular app. "Now you can sell copies of your app to two players instead of one," says Dave Howell, a former Apple engineer who now runs peer-to-peer file-sharing apps maker Avatron Software. In the future, a player may be able to invite another to a game when the second person does not yet own a particular app. Such invitations could trigger additional purchases.
Recommending apps to friends and getting the 5%-ish cut sounds like a great idea to us. There is nothing technically blocking something like this, and throwing a little change in my iTunes account for a recommendation sale sounds good all the way around.