As I mess around with all of the social media tools, the one thing I tend to look for is way to combine users and information. It could be driving links out and "hope for" the click through, or putting information out to where the people are. The goal being to find ways to aggregate information and users around single points of content.
So, as I was clicking around some this morning-doing my normal "make sure the world survived" I found this great road map on the exact topic from Kevin Rose of Digg. Its kind of long (26 minutes), but it lays out the issues and gives DIgg's perspective on creating the 2.0 version of the web 2.0.
The embed code is not working…so here is a link: www.viddler.com/explore/carsonified/videos/16/
So, yes, commenting and rating is a tool. Much like Twitter etc are tools. The end-game has to be a way to take the comments and ratings of the collective and tailor them to the individual. That is where discoverablity and usability break away–and true lively community is built.