We reveal so much more about ourselves than we could ever imagine. If you use, or used Reddit, Snoopsnoo [1] is a site that uses incredibly primitive language parsing to build a profile on users based on what they've voluntarily submitted. And again I have to emphasize that is using very primitive parsing. It's disconcerting how much we reveal when an algorithm is able to rapidly and effectively piece it together.
Now when enter the government that data can be cross matched against other meta-data to nail down your identity to a very small segment, if not outright match it. And then we get into things like language analysis. I make some token effort to anonymity, but my wife has mentioned she often knows its me posting before seeing the username. And I can do the same for other people I know well. No idea what we're picking up on, but it's a task that machine learning would be phenomenally well suited to do - and do better than we do. And then there are things like more explicit dialect issues. This [2] is a quiz based on American dialects. Again it is phenomenal how much your vocabulary, which undoubtedly you view as 'proper', actually reveals your location. Our very language is not only a finger print but also a geo-tracker.
[1] - https://www.snoopsnoo.com/ [2] - http://www.nytimes.com/interactive/2013/12/20/sunday-review/...