I wrote a book-length research piece on collaboration and I still can’t spell collaboration correct on a consistent basis (I misspelled it in this sentence the first time through). Part of the reason is that I always use a spell-checker. The other part is because my spell checker (GNU Aspell) is really good. No matter how much I mangle a word, Aspell almost always manages to suggest the correct replacement and it’s usually the first option. The end result is that it’s more effort to learn to spell the word correctly than it is to correct it each time.
If my spell checker was less good and I was forced to read through the entire list options or, god forbid, type in the correct spelling by hand, I would know how to spell more words. I think that the lack of improvement in a users’ spelling ability over time may be one useful metric in evaluating the effectiveness and efficiency of a spell-checking software.
I think my complete stagnation in the swamp of bad-spelling is a testament to Aspell’s greatness.