Oh, the other thing (used a lot with Twitter posts) are URL shorteners. Arrrgh! They're fine if you're trying to rick-roll someone, but I want to know where I'm clicking to, not see a bunch of garbage characters.

For a perfect example of the uselessness of twitter and replies and URL shortneing, see the Twitter feed of the otherwise excellent Strobist Bog: http://twitter.com/strobist