Facebook (and some other sites I use) recently "updated" its user interface. One of the changes was to "hide" the "Logout" button under a new dropdown menu. (A couple other sites have either done the same or relegated the logout button to another page entirely.) This decision is deliberate. Facebook wants as much of your online behavioral data as they can get. And governments want that data, too.
By hiding the logout feature, you're more apt to simply close the browser or tab, but effectively remaining logged into a service. This allows Facebook to openly track your online whereabouts via advertising partnerships that all report back to Facebook (a couple years ago, they called this "BEACON.")
A potential solution is Ipredator, an encrypted proxy from The Pirate Bay. I'm not sure how long this service will remain viable (the U.S. could simply shut off access at whimsy), but for the short term, it's an easy way to remove yourself from the trackable net. This is probably a good thing.