I've been using them for a few years now. Free repos got me there. Assembla makes use of it as well, and I've run it through that on a project. I don't do enough open source stuff unfortunately to find myself at Github, but for maintaining a bunch of free private repos its great.
Thanks for the correction. I made the edit above. Funny thing is that I had a feeling I was wrong, but general sloppiness convinced me adding a question mark to my statement was better then taking 10 seconds to actually look it up.
