What can people find out about you online? Well, why don't you do a cursory search for yourself? Try Piple.Com. Merely type in your first and last name and see what is out there in cyberspace about you. I was a little surprised to see a mugshot of myself -- one which I didn't personally posted online.
As an active user of the Internet it is no use trying to "hide" everything. Just be careful what you reveal about yourself. Don't reveal things you would not reveal to a crowd of people ('cause that is essentially what the Internet is -- a very big crowd). A healthy Online Profile is also a good thing. Future employers may search for your name and if they find nothing, they may pass you over as insignificant. You aren't insignificant are you?