While it's not surprising that some employers might want to snoop in your social media life, it strikes me as a remarkable misapprehension of what Facebook is to think that it should be wholly open for background investigations. Legally, things are probably more complex, but it seems commonsensical that carte blanche access to your communications should be off-limits.
The case also shows a downside to Facebook's scale. It stands to reason that the bigger they get, the more that employers and others concerned with the age-old enterprise of covering their asses will feel the need to know what their employees are up to on the service. That alone isn't going to derail the Facebook juggernaut, but it might slow down people's engagement on the site as they realize maybe a private, unknown e-mail account is a better way of sending sensitive messages.