The House of Representatives just killed an ammendment intended to make it illegal for employers to require that prospective employees hand over Facebook passwords before being hired, which apparently (and amazingly) is an actual practice at some government agencies.
Since it gives access to private correspondence, there's no fundamental difference between requiring an employee to hand over a Facebook password and requiring one for a webmail account like Gmail or Yahoo mail. And of course there's no fundamental difference between that and requiring employees to turn over the faxes they receive or the contents of their physical mailboxes for the employer's scrutiny.
I'm not a constitutional law expert, but I believe that the the Maryland Department of Corrections requiring an employee to hand over the contents of a personal mailbox under penalty of losing his livelihood might be a Fourth Ammendment issue. Witness the fact that we've had snail mail for centuries and employers are not making this demand on that medium (even the government). The difference is that Facebook is new, and therefore the people who are making these demands fundamentally don't understand what it is they're demanding.
This report is just the latest incident in a storied history of the U.S. government doing a bad job when it tries to meddle in technology. The unfortunate but undeniable fact is that since the advent of the personal computer, government policy has been unable to keep up with the progress of technology, leading to a long string of "doesn't get it" moments, typically involving trying to regulate or control what it cannot. Do we all remember the V-Chip?
When government is wise, it creates an environment that helps private industry and private individuals work out how to use technology best. When it is unwise, it makes ill considered decisions like this one.