The Almetric software shows "citation" data on scientific papers harvested from social networks such as Twitter, Scientific Blogs, Citeulike and Mendeley. They deliver this content via their very easy API.
You could also visit their website http://altmetric.com/ and enter a DOI number for your favorite paper and see how many citations from social network it has. Also you can see the "hot" papers that have the most number of citations so are the one that "everybody" is reading right now.
I am using the altmetric API for my website and noticed that there seems to be a mix up in the data that was harvested for one of our recently published papers:
Peña C, Malm T (2012) VoSeq: A Voucher and DNA Sequence Web Application. PLoS ONE 7: e39071. doi:10.1371/journal.pone.0039071
For some reason Altmetric started to collect data from their announcement when their released Altmetric:
You can see the Altmetric API and changes in their github profile: