Companies struggle to measure "Social Marketing" success, because they have no clear goal. Most Marketers are happy to just get increased web traffic. This stems from the assumption that revenue can't be tied to social marketing. My new company, Karmaback, can definitely fill the gap in measurement AND deliver revenue directly tied to social marketing. This feature, however, is irrelevant... because marketers don't have this as a goal (yet).
Instead, we at Karmaback have decided to focus (for now) on the goals that marketers do set: more fan growth (Facebook & Twitter), and more site traffic. We'll keep preaching that revenue should be the goal, but until our customers realize it is possible, we'll deliver results they "think" they want.