The fine folks at The Realtime Report have put together a very nice guide to understanding social influence measurement tools that should be rather helpful if you’re interested in understanding and leveraging influencers in your marketing program. And the fine folks at Appinions are offering a limited supply of those reports for free. Honestly, I missed this report when it first came out, but have recently read it and am quite impressed.
Not only is it thorough and thoughtful, but even breaks the tools (like Klout, Kred, Traackr and so on) down into personal influence and contextual influence spheres. I consider myself fairly well-read on the topic and I learned a few things here.