Measuring the ROI on social media must be done by more than looking at the increased sales and revenue. Social media helps to build and maintain your brand identity. It helps to instill and create the perception of who you are and what you are offering. It is like laying the ground work for recognition for your products and services. I will share with you an analogy.
In life, people get to know you and what you do. They learn this by what they see from you and what they hear from others. Social media works the same way. By placing information about yourself (or your company) out there on several different social media locations, you are building your reputation.. Then you are a part of a certain industry or a certain genre. You are who you are, built by the perception and reputation you put out there.
Here is another site that talks about the need to build and optimize your image in social media: