Mostly sensationalist fodder. Almost all companies want to track user habits on their website in order to see how it is being utilized. This is standard in the world of metrics. Just about every site you go to records your visitation path and that information is in turn analyzed and influences the direction of how that website could evolve in the future.
And honestly, I'm sure the FB message database is encrypted pretty well, just like any other high-profile company. And I would assume they have safeguards from letting unauthorized employees in there. (I would hope, anyway.)