Google just announced that in-app billing -- first announced at the Honeycomb event we were at in February -- will launch next week. In-app billing is an unsexy name for the way an app developer can sell you extra features -- levels, weapons, clothing, cheats, etc -- while you're inside the app. No diving back out to the Market, all seamless and smooth.
And to get things ready, developers can now upload and test apps for the service. It's all done within in the existing Developer Console, and the dev sets the prices.
It'll be interesting to see what sort of things developers offer, though we can think of one, for sure -- the Mighty Eagle! And Tap Tap Revenge will use it for song purchases. [Android Developers Blog]