Interestingly enough, most folks working on GitHub.com don't use this model. We actually use a simpler model, and usually merge to our feature branches rather than rebase. I'm not sure if Zach's latest talk(s) goes into this level of detail.

I think a big part of the reasoning is because we tend to push up branches really early to open PR's and get discussion going. And of course rebasing public branches generally leads to hell.

I know some other .com devs will rebase privately before pushing a large branch, but I would say 80% of work is just done with merging.