The issue of "reputation" is really interesting and my guess is that will be more and more important in the future. It is already important in specialized communities where it makes sense to be an expert or a master or a ninja or you name it or gain karma points.

But I am not sure how important can it be in communities with many many users and without a well defined focus. He refers to a few metrics for the social component but it is not clear yet what a good and appealing "reputation metric" could be.