E-mail is dial tone. Companies couldn't exist without it. Nobody would think about calculating its "ROI."
The adoption of social technologies in the enterprise is headed there. By the time your organization conducts one of those long-winded ROI analyses by an expensive consultant about whether to deploy social technologies, your competitors will have already done so. By then your customers will have already shifted their communications focus from email to social. By then your employees -- especially the young ones, but not only them -- will wonder what the heck you are waiting for and will have figured some way to end run the formal communications infrastructure of the organization.
Forget the ROI analysis. Before you complete the analysis, social technologies will be dial tone. Get on with it.
Very nice take from Jim Mancini!