TPMIdeaLab did a good interview with Reuters Social Media Editor Anthony De Rosa and asked about how he verifies social content: http://idealab.talkingpointsmemo.com/2012/07/reuters-twitter-anthony-de-rosa.php?m=1
"There are all sorts of digital footprints that come across with this sort of information. You can look at who’s following them, who they’re following, how old the account is, look at the history of messages they’ve left over time. It’s almost like a forensic analysis you can do. I look at whatever information is around the account I’m looking at. And I also find Storyful really useful — they have people who can often find the actual person behind the account, and they can get you the phone numbers, email addresses, and over time they’ve actually built up a rolodex of sources who tend to use social media directly, and you can reach out to them and do a little bit further research on them."