The NetBeans folks have a very interesting collab module. It was designed to assist remote peer-review of code. The model is really cool. You take a file and share it with others. The shared file goes into a "sandbox" so your original is not modified. Everyone can collaborate in the sandbox. Then the sondbox file changes can be merged back into the original file. This could even help assist remote pair-programming (something I've been experimenting with).
There is an article about it here... http://www.artima.com/forums/flat.jsp?forum=106&thread=117079
The collab project is here ... http://collab.netbeans.org/. You can see a demo of it. Just look under "Getting Started" for the "See" link.
If only it worked in IntelliJ and Eclipse.