The checkout lines that say "10 items or less" are grammatically incorrect, and the people who know of this like to point it out with much grandeur and pomp.  Less should be used with things you measure (less coffee, less talking, less annoying) while fewer should be used with things you can count (fewer items, fewer baby-eaters, fewer exploding M&M's).  Oddly enough, the opposite of both less and fewer is more, thus adding to the confusion. #language