Inspired by some posts I just read - incorrect spelling of words that results in distortion of meaning drives me nuts:
MAT - a woven surface to sit on, a border around a print, a padded sport surface, whatevs - generally a flat surface that covers something else
MATT - a shortened version of the name Matthew
MATTE - a dull finish on a surface
When did it become acceptable to substitute the first two for the third without any regard to meaning?