Indeed, while 19 seconds for commit is far better than 30 minutes we would have seen without GVFS, it's way too slow to actually feel responsive while you're coding. And in fact, it was sometimes worse than 19 seconds because commands like status and add would generally get slower as you access and hydrate more files in the repo. With the big O(modified) update that we just made to GVFS, git commands no longer slow down as you access more files, so now our devs see a consistent commit time of around 10 seconds, and consistent and faster times for most other commands too.
You have to put this into perspective with what they are replacing. You'd never get a submit done in less than 19 seconds using the old source depot tools anyways. When you work on projects this big that takes hours to compile and minutes to incremental compile - responsiveness just isn't something you get to have at scale.
This is mainly why I'm asking for data from Facebook. I've seen claims that their vcs operations (at least the most common ones) are near instant, but nothing official. It would appear that FB have solved the responsiveness problem with Mercurial but, again, no official data to back it up.
