I always wanted more dynamic commenting which some of the fisheye/github tools already do. For instance being able to have a discussion about a line of code. Not necessarily a code review, but more like explaining the code with pro/con discussion if necessary. It is a bit troublesome to implement you always get snapshots of code, so how to track lines. Plasticscm seemed interesting, http://www.plasticscm.com/gallery.aspx, but I think they are aiming at the Microsoft crowd, git is pretty firmly entrenched otherwise. Looks like they tried to learn lessons from git and it's success.
