If an employer (or potential employer) wants to know about my private life that badly, hire a PI. At least then, digging into my private life is going to:

A) Cost them money

B) Not get them everything unless the PI follows me around for a year or two

The closest equivalent I can think of for something like this would be me asking a potential employer for the password to their Sharepoint / Wiki / company electronic bulletin board system / internal forums. After all, if they want to poke through my personal information before deciding to hire me ("We really like you, but those drunken photos from your spring break at that Hedonism II resort just don't fit with our corporate image. We know those were taken 15 years ago on your first spring break, but...") then I should be able to look through their "personal" information ("Well, I was really looking forward to working here, until I saw the posts on your forum from the staff of the department complaining about the constant direction changes, projects being cancelled one day then started back up two days later, and regular 16 hour marathon work days.")

I take keeping my work and private lives quite seriously, I do not "friend" anyone from work on Facebook, and I do not post anything on LinkedIn that I wouldn't want co-workers to see (considering I don't think I've ever posted anything to LinkedIn...)

As it is, I really only use Facebook to keep up on what the rest of my family is doing, and while I've got some photos up on Facebook, they're of things like family get-togethers for X-Mas.