I would like to add to Vadim's comments. The component of social networking mentioned is in the 'observed' space. This was a very successful promotion for the Palm Pilot mnay years ago. I think most marketers now focus their thinking on social media as it pertains to the web, but they are missing components that bring the real world into it as well.

Actually (in response to John's question) it would be interesting to hear if anyone is using Net Promoter Score as a measure in the social media space, although I'm not sure how it would apply, since it is a much higher level metric.