Seems pretty straight forward to me. If you use their network, you play by their rules. Not discussing work outside of work is nothing new. You wouldn't go downtown and post internal information about your copmany on a bulletin board or telephone pole, why put it on Facebook or Twitter? Seems like this is mostly just common sense. They probably need just to have it in writing so when they fire you for being on Facebook all day they have something to cover their asses. C.Y.A. That has always been policy in any business.

You had better take a look at this http://www.cbc.ca/money/story/2007/06/13/canadapostups.html. UPS didn't WANT to compete, they wanted to sue. Just like everyone else.