I think it's very hard to conceptualize just how valuable and/or powerfull that data can be. Especially when it's given away in small pieces; Knowing my birthday by itself is useless, and so when some webform asks for it I all too easily think it's fine to give away without a second thought.

The same can be said for someone wanting to keep their location private; It's harmless to let the public know you live next to a park, and it was relevant to the story you wanted to tell that day. A month later you complain about the noise, and someone links that you may be near a highway. A week later you complain about a storm, even going so far as to live tweet it from the comfort of your own home, at one point tweeting "wow the rain got real loud for a moment there. Glad to have a nice house :D".

And now Mr. Dedicated Bad Guy has a list of three locations your house could be, all from seemingly innocuous information.