While not yet as far along as other social media experiments for books environments (like Copia) the tool has the same idea at its base -- enabling communities of conversation around digital books. One aspect of the Readum approach that I like is that they are actively working to demonstrate the "proof of concept" by utilizing existing social networks rather than trying to build their own. That enables a more coherent strategy and focused development around competencies. It will be interesting to watch where this project goes.
A short video on Readum appears below: