Free speech is like a dog in a minefield. It's fine until you try to exercise it. Telling a friend your opinion is fine; texting that opinion to a stranger is risky; putting it on Twitter for the whole world to see is asking for trouble.
While it is obviously tempting for bored HR executives to spend the day Googling employees or harassing Facebook in the search for some dirt, the inevitable consequence of this is that social networking sites will just become extensions of our CV. Everyone already bigs themselves up, of course, that's just human nature. But the kind of bigging-up you do at parties and the kind you do at job interviews are very different:
"I'm a netadmin, which mostly involves being paid to reset passwords for morons"
"I'm a senior network administrator at a Fortune 500 company"
are essentially saying the same thing, ie nothing. It's just words that you say to create an effect. And that's Twitter in a nutshell. When you say "I'm in one of those town's where I scratch my head and say 'I would die if I had to live here!'", what you really mean is "I can't think of anything funny to say about Memphis in 140 characters". Which is itself, just a long-winded way of saying "I'm in Memphis."
And taking offence at that kind of comment is entirely lame. Visitor to your home town doesn't like it and you want to get him fired? Jeez guys - sense of humour failure!
"Don't say anything on Twitter that you wouldn't say in person" (NSFW) is a good rule. But when that becomes "Don't say anything on Twitter that could ever offend anyone ever", it's time to stop saying anything on Twitter.