I just got my invitation for CoComment (plenty of posting on this). As I registered, I realised something important - this has the potential to make me comment more. CoComment provides mechanisms for tracking and sharing conversations you participate in the form of comments to blog posts. These are captured by a bookmarklet that you hit whenever you make a comment. Generally, the introduction of an extra step means a change in behaviour and consequently a barrier to users. It will be interesting to see if the CoComment mechanism is going to break through this barrier.