Hm, AFAIK, we don't record the data that would be required for this. Maybe it would be interesting to have that data for other reasons (putting that info on the stats page, etc?)
Maybe. This is going to take some significant effort in researching how Facebook/Twitter surface this data. It's non trivial, but doable. My vote: Up for Grabs unless people chime in and say they want it.
This issue goes in this direction #638
For Twitter there is an "unofficial" HTTP endpoint - the twitter button uses this and it requires no authentication or any fuzzy Twitter Code:
For Facebook we could use the Graph API: