Okay, maybe not ever but thanks to a local colleague, Andrea Goulet we uncovered the Centers for Disease Control's (yes, the infectious disease people) Social Media Guide.
It is a wonderful style guide that details voice, language guidelines and has sections on how to write for facebook and twitter.
My favorite part is Chapter 8 which challenges you to rewrite the poorly written tweets and messages. All in all it is a bundle of helpful tips and tricks written in plain language. So grab a cup of tea and dig in. We dare you to read it and not find it useful.