[pitoufsd]

For me, it's reading something by someone who doesn't know (or care to know) the difference between 'than' and 'then.' The problem with misused 'thans' and 'thens,' is that they are usually not immediately identifiable as being improperly used. It's only once you read on (either the comparison, or the next event) that you realize the author's previous error.

"I would rather buy a Matrox Parhelia then give my money to nVidia because I hate nVidia."

Wait, what?! See! It's only once you read the end of the sentence that you realize the author's laziness. Makes me want to throw an axe through my monitor, except that I don't own an axe and I'm quite fond of my monitor.

EDIT: I propose a new auto-correct feature. Whenever 'than' or 'then' is typed, a little MS paperclip should fly over the text box and say, "Hang on there, slugger. Are you sure you didn't mean than/then?"