Klout can be helpful as some measure of influence or even just as an overall measure of how well someone is doing with engagement and interaction. I also like Twitter Counter and Tweetreach. Facebook Insights offers quite a bit of helpful data and if you use a link shortner that allows you to track clicks that's another good measure. Other than some paid tools, you really sort of have to put together a list of sites to create a good overall picture of social media efforts from different sites.
Kimberly posted on the Business Darlings site a great article entitled Can You Measure Your Influence on Twitter which may prove helpful for measuring Twitter SMM influence.
Janine
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