[cuddlypsycho]

I'm not talking about email, IP address or any other convenient mode of identification.

Think voting patterns, date/times active, submission categories, comments, writing style, punctuation ...

Facebook had a project to cross-reference user behavior to anonymized medical data. Say patient A's history says he visited a foreign country in the Mediterranean, came back with the stomach flu, was hospitalized for 3 days ... Maps to: holiday photos, dates, locations, status updates, friends commenting get well soon etc.

I hear they were pretty successful at it too! Makes you think what a government actor can do with enough data.