I once had experience of writing "collaborative" text in LaTeX by using [subversion][1] -- a software versioning and a revision control system for program-developers. That was really cool! Everytime you have the most up to date version. All the "collisions" are dealt with automatically e.t.c.  

The problem is -- all your collaborators has to be familiar with this software and the concepts. That's why I had such experience only once. 

But I still use it for my own projects -- I setted up repository on my usb dongle, so I do not depend on the computer I use...  

 [1]:http://en.wikipedia.org/wiki/Apache_Subversion