Mike - all spellcheckers have the ability to add words to the dictionary which it will then check against.

I have worked with Estate Agents software for 15 years and there are lots of instances of spellchecking amusements. A self-professed poor speller had added all her wrong spellings to the custom dictionary so that it took all her misspellings as being correct.

I agree with the person above. It is partly about spelling but a lot about grammatical and sense errors. If you take the use of 'could of' for 'could have' - it passes the spellcheck but is grammatically horrible.

On the Estate Agent line too there are a lot of agents who will either dictate the house details or use speech recognition software. If you type from dictation it is easy to hear wrongly.

I can spell well (who can't, it's only got 4 letters?) but typing is an easy way to go wrong. Especially if I'm in a hurry.