There's already one site that I've changed my sign up address for, because of this kind of thing. I may yet change more (I also changed Facebook). Yahoo also wants you to have a profile, but I managed to hide mine.

As a word of caution, I spent an hour chatting to a stranger, didn't know their first name, but knew their hobbies and what they did. As a test of google fu, I tracked them down. In about five minutes.

(I'm not normally a stalker. Honest.)