If GitHub was open source, we wouldn't be able to make money to hire people to make awesome features. An Open Source GitHub would without a doubt be a much worse experience for everyone.
Gitorious is 8 million time better than rolling your own git hosting, but GitHub is so much more polished. I think a large part of that is because Gitorious is open source, so there's nobody dedicated to it as a full-time job. Whereas you guys have a handful of developers working night and day on creating pure awesome.
You guys rock.