After promising imminent launch last week, Google has flipped the switch to turn on in-app billing across the Android Market. Developers can now choose another source of revenue as an alternative to charging up front or relying on advertising in the apps themselves. A number of games such as Tap Tap Revenge (pictured - read our hands-on from the Honeycomb launch event here) and Gun Bros already support the service (along with Comics; Deer Hunter Challenge HD, WSOP3, and Dungeon Defenders: FW Deluxe), and more developers will certainly add support in the coming weeks.
UPDATE: Check out a couple more pictures past the break. [Android Developer Blog]