About a decade ago, it was important to stake your presence online, as there was quite a land rush to do so. i know i have dozens of accounts all using the id of "jrconlin". Now, it's equally important to hurry up and create something far more critical; you need to create your fake persona.
Facebook, Google, and lots of other services are all pushing for your information. There's arguments that this may help keep John Gabriel in check, but in reality, it's more to do with making you and the network of people you know higher value. Obviously, there are lots of other parties who would be very interested in what you're interested in. And, since you've nothing to hide, right…?
For now, it's impossible to say what your personal information is currently or will be used for. You simply don't know if your actions are raising red flags, or you're being a person of interest. On a less paranoid note, it's also kind of a pain in the ass to go try and read some article and have an idiot marketing weasel hit you up for a "Like" or "Tweet this!" before you've even got so far as the headline.
That's why i have a few fake personaes (No, i'm not going to link to them). These are names i generated, with equally randomly generated information. Naturally, some sites are making it increasingly difficult to create a fake person, and are requiring things like a credit card number or cell phone number which might take a bit more effort to get around.
My fake person gets her own browser (or browser profile for those that support it) where she is logged in to sites various sites long enough for me to get what i want and then leave. i tend to use her when visiting new sites to poke at things and see if that site has earned my trust (or at least provided enough value that i feel i could use it). Most of the time, the answer is "no".
The problem is, i can see that more folks are going to build fake people. Which means that it will become harder and harder for new folks to create new fake people. Fake folks may be "grandfathered" in solely because it's so hard to tell them from the real people. It may well be that parents will bequeath their fake person to their children so that they can have some shred of privacy in the future.
Sorry, folks, but you've not answered why you need to know what i have to hide.