I went to graduate school with a guy who ended up on Google's infrastructure team. He'd previously worked as head or lead dev for subversion (a little hazy on the details).

We worked on a small project where we put together statistical measures for codebases. It was a lot of fun, even if the infrastructure was out of my wheelhouse at the time.

Folks that can manage billion-line codebases are on a whole different level I think. I wonder sometimes how many folks like that there are.

EDIT: Looks like he left for a bit and is now back. Good on him!