I like having automatic spell checking when I use FireFox, but I use it as an aid, not as a crutch. I'm not a perfect speller, but most of the time I spell correctly the first time. Besides, spell checkers won't catch everything. For instance, a very, very common error is to use "loose" where "lose" is needed. Since they are both words the spell checker won't mark them as misspelled.
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If ye love wealth better than liberty, the tranquility of servitude than the animated contest of freedom, go from us in peace. May your chains sit lightly upon you, and may posterity forget that you were our countrymen! - Samuel Adams
I used to be a very good speller, but spell check has definately hurt my skills. Now when someone asks how to spell something, I endup having to start something with a spellcheck to verify the correct spelling.
Of course my biggest weakness is from my second language. Since nouns are capitolized in German, I always have to go back through whatever I type and remove all the extra capitolizations.
