And I personally know a couple of people who have had offers for employment/internships rescinded due to "failing" the FB background check. My mother works as an HR director for a semi-well-known company and is insistent that my brothers and I be particularly discerning with what goes on our FB pages as SHE has refused to green-light the hiring of employees due to the content of their social network sites.
My "concern" really only goes so far as to not being one of those people whose profile picture is them ripping a bong, using proper grammar and untagging myself from the occasional photo or two. I don't own stock in tinfoil, so I'm not going to go overboard ranting about The Man being out to get anyone. As far as what this particular engine digs up: obviously there are various bits of information that can reasonably be expected to fall beyond one's control as far as protection is concerned, but it certainly doesn't hurt to remember that shit doesn't just vanish once it hits the web.
My guess is that before long the whole address, marital status, estimated income, etc. crap will seem remarkably tame as to what will eventually be available as the software and resources become more sophisticated. Remember Tribunal Dude? I believe HE was able to scrounge up the online and "real life" identities of a few posters back when he frequented this forum (maybe with Oleena, perhaps? He had a grudge against her, if I recall correctly.), and that's just one nut job with too much time on his hands.