A spell checker would be nice, but an automatic spellchecker would be an annoyance. I would not want to have to tell the spellchecker to accept my spelling every time I mention a user handle, use 1337, or use an ancronym the spellchecker does not recognize.

Some of these issues could be easily resolved. The spellchecker could have all the user names added to it's dictionary, and it could accept all acronyms by default (denoted by all caps), but that would dilute it's strength.

I would rather see a strong voluntary spellchecker than a wimpy mandatory (automatic) one.