Social media is about connecting with people on a more intimate and individual level than mass media. In the past, companies spoke at their audiences through advertisements and other marketing forms. Now, companies can INTERACT with their audiences, in fact making communications more of a two-way phenomenon.
With that in mind, the closest comparison to social media is in-person networking. I wonder how many companies calculate the ROI of sending a company representative to a networking event. If the person makes ten connections but no sales is that considered bad ROI?
Networking, and social media, is about building connections. There may or may not be a dollar value that can be attached to those connections.