Hmm, I don't know about the rest of you, but when I'm typing a lot, I generally don't make the same mistakes. Ok, when someone consistently misspells the same word, its probably because they don't know how to spell it, but what I'm getting at is, that I more often than not just hit the keys in the wrong order.
When there's a lot going on in a forum (or Mud, whatever) then one tends to get out as much as possible in order to keep up, which produces a lot of inconsistent misspellings. (It does in my case anyway, I'd be glad to prove it).
Which makes me think that comparing misspellings is not such a good way to do it.

Example: German word 'erzaehl', comes out as 'erzahle', 'erzeahl', 'erzaelh' etc. (I've even made aliases for most of these ;)

C.