I was trying to catch up with my reading on some print magazines related to my paid work, one of which is "APC" (Australian Personal Computer), May 2012 edition. There was an article in there entitled "Hashtag Errors" which discussed the various PR disasters that have happened on Twitter for companies like MacDonalds, Coca-Cola and others. The article included this advice to people in marketing or PR:
Don't try to use the social media networks to put a spin on a story or to lie to customers. They are the ones who own that forum, not you.
That last sentence in particular seemed like advice that was sound and applicable to some of the discussion this thread.