Anthony Towns:

Writely, the web-based word processor, was kind-of interesting, but in the end didn’t work for me. The potential killer feature for me would’ve been SubEthaEdit or Gobby -like interactive collaboration, which seems like something Google ought to be able to do with their whacky AJAX techniques. Unfortunately, it seems to just be some sort of automated merge-on-commit, which does nothing for me.

I believe Writely’s attempt at real-time collaboration is a little more advanced than merge-on-commit, but as far as I know it is based around diffing instead of actual change tracking. The trouble with this is that it makes it nearly impossible to preserve the user’s intention rather than just the effects of the operation. It’s certainly easier to get a system up and running using diffing than using actual tracking of changes, but the results just don’t sync up with what users expect as much and I suspect Anthony’s experience reflects that.

Having spent a heck of a lot of time working on track changes now, you’ll probably hear a lot more about it and Is suspect actual tracking vs diffing is going to be a common theme.