I think it's a great idea as well, although I'm not certain exactly how to do this in Mercurial.

Originally I was going to use branches to indicate releases, much like LJ has been doing for the past few years. When I tried to play with the branches though I ended up doing something wonky and not really understanding it so haven't been back to that yet.

Anyway! Great idea, would love to do it, suggestions on exactly how?