I couldn't agree more. We're all here to communicate, so why not make it as easy to understand one another as possible?
What you post and the way you post it is the only way people get an impression of you when you're online. I can only assume that since you don't have to meet face to face the impression you give doesn't really matter.
While I'm at it here are a few other things that piss me off;
Huge signatures.
If I'm interested in all the s*** you've done to you car I'll check your profile. Don't waste precious bandwidth with a list of every car you've ever owned, every mod on you've ever done and every mod you intend to do. It's not relevant to every post you make so don't make me wade through it every time you post! If you slap a huge pic of you car in your sig you deserve a dick punch.
Abuse of Smilies or Emoticons.
Use them to show emotion to help people understand your tone.
For example, if you're being sarcastic use this guy

Confused use this guy
If you use more than 3 emoticons in a single post go get some lithium to sort yourself out, you're feeling too many emotions at once.
Neglect of the search function.
Use the search or get a dick punch. Your call.
Ahhh, that feels better.