Via Silicon Valley insider comes this marvellous chart which reveals people do more sharing of links via Facebook than they do via email. Just ignore the headline on the graph.
What's particularly interesting to me is the volume generated by Twitter - which has approximately (and likely less than) one fifth as many active users as Facebook right now (roughly 45m to roughly 250m).
Which means the adhoc fuzzy-edged communities of purpose who populate twitter are around twice as likely to share as those of us (often the same people) restrained by the private-data-heavy silos of friends on Facebook. Nutshell: You're potentially twice as likely to learn something new on Twitter as you are on Facebook.
Open beats closed when it comes to learning and sharing new stuff. Case, ah hem, closed.