According to an article in the Times Higher Education Supplement, common spelling mistakes should be accepted into everyday use, not corrected.
Ken Smith a lecturer at Bucks New University says the most common mistakes should be accepted as "variant spellings".
He lists the 10 most commonly misspelt words, which include "arguement" for "argument" and "twelth" for "twelfth".
(Maybe I should stop correcting mistakes on the forum.)