Well I happen to totally agree to every one posting before me - a spell check might be quite useful. So many people have to write while being in a hurry and so mistakes happen or some people have a lot of grave mistakes in their language and that would actually improve their writing quite a lot.
I second that... I would like to spell-check my websites from the crawler's point of view to make sure I haven't made or failed to correct mistakes. Google takes spelling too many mistakes into account now.