ROI is the correct measurement for strategies like search engine optimization, pay per click and web traffic, but when we talk about social media it is not easy to measure. Yes, you can measure followers, friends, references but matching those to sales and profits is not always easy. There is definitively ROI in the social media space but because social media is innovative and relates to things that are new, there is no past history to go off of. If you are trying to justify a social media budget and your superiors want to have support information from past executions, you are goint to have a tough time.
Often times we bring innovative strategies to clients, they say great, who else has done that, so we can see how they did? Or why can´t we do the same thing as these other guys did? And they want to replicate. But the reality is that social media is such a virgin terrain with so much to innovate that it is difficult to always be showing past examples or past success stories. So a wise piece of advice is that when you approach social media, follow your intuition, release your creativity, assign a good will budget and follow the best practices known today. Then measure results, followers, links and repeat again; your ROI will come from improving in every cycle and setting your own metrics. The bad ROI will come if you do not do anything. Do not be confussed, you have to measure, keep track and compare results with every execution, just do not be obsessed with traditional ROI because very probably you will not be able to relate followers to profits, or at least not precisely as you do for example in SEO campaign for an e-commerce site