I have a site that is popular among a certain demographics and I mostly get my natural external links from social sites such as stumbleupon, yahoo answers, wikipedia, forums, etc. It seems that these sites have replaced the small sites from your average joe, like geocities some years ago. However, all these sites use the nofollow attributes on links nowadays! They do bring a certain amount of traffic on their own, but isn't Google missing on a lot of that action by not taking this new web 2.0 dynamic into consideration? I know they're possibly easy to spam, but still, there must be some value to this data. Meanwhile, it's becoming a handicap for my site where the popularity of word of mouth does not have a corresponding improvement in the SERPS.