Google should acquire GitHub and let the GitHubbers run Google.
I know! It would be horrible to have the service be free, and integrated with Google's other search and social features and therefore more visible to the world!
THE HORROR!!1
[edit: not to mention company lawyers looking to sue some NDA violating employees]
Perhaps you could grep for common libraries like "ffmpeg" and make a guess as to what sort of software it is. Maybe a video editor/player in the case of ffmpeg. Once you figure that out, you could show advertisements for the same sort of software.
So it's already free, it's already integrated into Google's search, if I want to be social about what I'm coding I can easily share it on G+...
What problems would be solved by doing anything differently?
If Google bought it and nothing changed I'd be happy!!! However, I don't think that'd be the case. Things would change and I suspect for the worse, since it's not a big cash cow like search is.
The biggest problem with google acquiring github is that github would be expected to integrate with google's infrastructure; which would be a monumental engineering task. I can't see that happening in any way that wouldn't hurt github somehow. The best case would be that months of github's engineering time is taken away from new features. The worst case is that github is integrated with google code somehow; which would probably result in a revolt by github's users.
I think an acquisition by google would only hurt the open source community. Google likes us too much to risk that.