There are some words I frequently get wrong on the first try, but looking at them I know they're wrong and go back and fix them.
My internet posting has probably improved fivefold since spellchecking became a common feature in web browsers. The problem is I post a lot about video games, and the spellcheck doesn't recognise words like multiplayer. I feel a bit guilty about leaving wavy red lines when I hit submit.
Also, I'm Australian and the software is American, so it doesn't recognise recognise, either. I refuse to put a z in there!