Gitosis is great, however I like Gitolite much better (ironically enough, hosted by GitHub - http://github.com/sitaramc/gitolite). Per branch permissions, and a much more intuitive project management.
I mean, I've been using GitHub 15 hours a day for a year, and last week was the first time downtime affected me, and even then I just couldn't push for awhile. That's kind of the whole point of decentralized version control right? So there isn't a single point of failure? I'd say the git ecosystem worked out just perfectly.
I'd say that if someone doesn't find GitHub's feature set to outweigh the level of downtime I've experienced, that person's use pattern probably doesn't fit the characteristics of a typical user. If I'm wrong, expect people to be leaving in droves now. My bet's on not.
1. You're hosting websites via GitHub pages.
I'm hosting both my business and personal websites on GitHub. (Despite the recent outage, GitHub's uptime beats my previous el-cheapo host by a wide margin.)
2. You host client code and issues in a GitHub private repository.
This becomes an issue when clients want to add a bug to the issue tracker, etc.