The Interactive Advertising Bureau has released its "guide to social media measurement." That's actually a misnomer. It is not a guide to overall social media measurement. As might be expected from any organization that has Advertising as its middle name, It blithely assumes that all social media interaction is desirable, and I can think of any number of organizations, from Groupon to Hosni Mubarak that might beg to differ. So, to be clear, if you are trying to measure the effectiveness of your advertising spend in social media, this is a good place to start. And the really good news is that it pretty much lines up with what we in the Social Media Measurement Group of the CIPR and the Validated Metrics Framework that came out of the Barcelona Principles.
Perhaps the best parts of the Guide is in the appendix. There are some good case studies and implementation scenarios that can help you get your mind around the problem.