My company uses GitHub internally. We have a "normal" mixture of senior engineers, junior engineers, and contractors.
I would love to use the GitHub Pull Request model, but it basically has a problem with spam. We would like the senior engineers to do code review and approve changes on a few 'sensitive' core repos, but GitHub emails everyone who has access to the repo.
So... if they introduce a regression that breaks GitHub they can't repair GitHub anymore? :)
When you eat your own dog food and some poison gets in, you die and can't fix it.
Our deployment process operates outside of our traditional network setup. If, for example, we push a change that breaks repository serving for everyone on github.com, we still deploy as normal and won't be impacted by it.
For something that could break GitHub, I'd hazard a guess that they'd deploy that as a branch without merging or to a subset of servers first. In addition, their deploy tools are built off Capistrano, not off GitHub (except for the Git bits, of course).
Same talk different location, but hosted on Youtube : http://www.youtube.com/watch?v=m7r2X9qC8jo
from post on Zach Holman's blog : http://zachholman.com/talk/how-github-uses-github-to-build-g...
previous discussion : http://news.ycombinator.com/item?id=3024588