I'm generally trusting of all things Internets, including Google's all-seeing eye (well acquainted with the collective id), but it's not a bad thing to be a little standoffish in knowing that the privacy rules governing the web are largely unwritten, or rather, being written by the companies you use everyday on the Web (Google, Facebook, etc.). Your guardedness should arise from the fact that they are attempting to create a market-driven, self-interest supporting code of conduct that balances their business interest against the whip of torts. As with any pioneering enterprise, the law isn't yet advanced enough to cover this ground with prescriptive rules simply because the list of contingencies is branching and broadening everyday with no signs of slowing down or normalizing. So the shake-out of privacy protection will probably happen by dint of these companies being called-out in court for bad behavior, aka violations of your privacy. All I'm saying is be careful how much you share since Facebook is working mostly to capitalize on your personal information as their marketable data. This should bother you only so much as you have ignorantly shared compromising information. The upside is relevant advertising, the downside is martyrdom in the courts. As always, the ancient writ of caveat emptor applies.
In these instances, I like to fall back on the rhetorical utility of my run-in with the naive young coed Boobs McGee, whom I interviewed several years ago at a campus recruiting visit to an elite college in the Northeastern United States. Before the interview, I received a dossier on Ms. McGee (actual name forgotten to protect her identity, which, on second thought, why should I work harder to protect her identity than she does?) with her resume and cover letter.
Naturally, I Googled her and found her Facebook page entirely too-open to the public featuring a profile picture of her busting out of a slinky black dress with some frat-guy chomped down on the upper-middle camber of her cleavage. Whatever her name was, 'Boobs McGee' she instantly became and the jettison of respect only quickened when her self-reported 'interests' included 'My Tits' and 'Cocaine.'
After the interview, I consulted with the career services folks and let them know that Ms. McGee wasn't quite right for us but might be better-suited for one of the open (and far more lucrative) Tiger Woods' mistress roles. Additionally, her professional faux pas might be cited as a parable to all undergraduate job-seekers as to the dangers of over-sharing via Facebook.