This weekend I got a chance to play around with ScribTex which is a tool for collaborating on LaTeX. In my short test drive, I will say it’s one of the better solutions to this problem that I’ve seen.
(Of course the one thing that is a pain with all of these systems is the lack of good editors. There is a certain handicap that you get by working in a browser input box and not into a full fledged editor (a similar setup to scibtex that I use in MediaWiki has this same problem.) I’m not sure how solvable this problem is. Has anyone seen, for example, a javascript solution which allows automatic syntax highlighting, for example?)