My wife started out with www.writelatex.com to write her dissertation. The auto-compilation really slows down once you get beyond 30 or so pages.

Also they don't have Git integration either, which was a deal breaker for my wife.

She's since moved to using RStudio locally + Git.

She says, "If you have Git integration, the auto-compilation feature would get me back from RStudio."

We've also thought about using Grunt to build our own auto-compilation feature.