Just introduced in the House is H.R. 5050 - Social Networking Online Protection Act (SNOPA). It's a pretty straight-forward bill (read the full text). Basically, an employer can't demand that either an employee or prospective employee hand over their passwords for personal email and social media accounts. Further, an employer can't punish an employee for refusing such a request (that demand is in plenty of company policies already).
For any of us that have spent a significant of time online, these demands have always rankled and seemed overreaching. After all, you wouldn't ask an employee to hand over their personal mail, would you?
Since most of my friends are either occasional or even reluctant Internet users, I think I can see the employer's viewpoint. There have been plenty of mainstream media news stories about people being caught because of embarrassing Facebook photos, or blog rants, or even tweets. A good number have been disgruntled employees venting about their bosses is a pretty public fashion.
I can easily imagine an HR administrator (such as one of said friends) who lets an assistant deal with all that interwebtube stuff thinking it would be a good thing to monitor employee behavior online. And the only way to do that, in their limited worldview, is to access the employees' accounts. I really believe these policies were created by folks who have little or no knowledge of how social media works.
Why? Well, because an employer can find out everything they really need to know by simply going online themselves. Look up some people you know on Facebook that you're not currently friends with. Sure, some accounts are wide open with pictures of bachelor parties and everything else -- but then there are others that are locked down. You can't see the information unless you're their friend.
And if a company is concerned about the image an employee might project, I think that would be a good sign. Sure, the company can't see what's going on in that person's life -- but the general public can't either. And that's really all the company needs to know (in my opinion).
Twitter's a little different. You can't filter who sees it. So foolish people will crack on their bosses -- and get caught. Others will be more discreet. And again, that's all a company should be concerned about.
LinkedIn is a little different. Since it's basically a job search site, everyone's putting their best foot forward. But it might be worthwhile for companies to check and make sure that the LinkIn resume matches the one the prospective employee gave them. But if there's information blocked, than so be it. On LinkIn that's a disadvantage to the user -- the ones who get the most out of the service want prospective employers to see everything.
Google+, in my opinion, hasn't reached critical mass yet. It's a lot like Facebook in that there are circles of friends, and you can set different privacy levels for different groups. Again, as an employer I would just want to know what an employee allows to be public (and hopefully not that NDA).
What I haven't seen in the discussion is Pinterest. Pinterest boards are pretty public. They can give you real insight into a person by seeing what they consider of interest. Sometimes you can learn a little too much.
While I think some folks are starting to think carefully about what they post on Facebook and other places, Pinterest choices seem based more on the Id than the Ego. It may be where your employer can find out more than you want them to know. And they won't need a password to see it.