Many people have gotten fired after ranting and raging about their bosses and jobs online. More are about to go in the same direction, no thanks to this web app called FireMe! It basically parses Twitter to collects tweets from people who are talking sh't about their bosses, their jobs, or both.
The tweets are then displayed on timeline for the whole world to see. And yes, that includes their bosses.
They might call FireMe! a 'service', but it sounds more like a snitch to me. But it's also a snitch that can save your job. If you sign up on the site, they'll send you an alert when they catch you posting job-threatening posts that are best kept private--so hopefully you can wipe that status before your boss comes across it. That's only if you're not hatching some sort of ploy to actually get yourself fired.
For all your other ranting needs, there's always Reddit.