There were systems that allowed you to mirror portions of piper into local git repo, giving you a git-like experience on top of piper, but the underlaying system was piper and not git. (At this point my knowledge is 4 years out of date.)
Various customers with repos in the PB range these days (metadata TB).
Disclaimer: current Perforce employee
That's a claimer, rather than a disclaimer!
"we went from seeing the server blocked routinely for up
to ten minutes at a time in 2005 to gaps of thirty seconds to a minute in 2010..."
CVS was nice(ish) since changes were independent, any number of people could check in code to limit of io parallelism. Svn was nice, the server would wait for a lock and if my changes didn't conflict, they would be applied after the rest of the pending commits. Git is a PITA, large companies build elaborate systems to queue commits, but we're not big enough to use that yet.
Edit to add: We may be "doing it wrong", but this is the least effort way to do centralized development.