Version control is a good feature. I read that sharelatex.com is working on adding git based versioning but currently there's not much information about it.
It seems that there isn't an online editor that currently supports versioning through git/hg, which is too bad
I've spent many restless nights thinking about how to best integrate git and a web latex editor. It's a hard thing to do as there is a clash of philosophies. The web latex editors are about making your word processing as simple as possible with minimum required knowledge and effort. Git on the other hand requires a working knowledge of the Git versioning model before you can start doing anything with it. Forcing Git upon unfamiliar users would scare them away.
