Ask/Suggest HN: Social coding with game mechanics

After spending some time on Stack Overflow, and seeing the extremely fast error->fix->commit cycles on PyPy development, I wondered, wouldn't it be great if there was a place where fixes, tests, merges, and documentation of a collaborative open source project was peer reviewed and awarded with Karma? With Stack Overflow using their points in their Careers section, there is even more incentive for people to contribute. I can imagine extremely fast development of complex software with this. Some details like who maintains the head branch etc., have to be worked out, but what do people think? Does something like this exist? Will someone try it out?