Ive written earlier about apostrophes, but now we have the definitive essay on the subject for all the peevers and prescriptivists out there: “Thats all Folks: The Apostrophe Protection Society Gone for Good” by the distinguished Dennis Baron. Read it slowly and carefully.
Be sure to read Barons last paragraph:
Never fear, English will muddle through despite their efforts to thwart its speakers and writers. The pedants will succeed in one thing, though: making users of English feel insecure. But until they do, Thats all folks!
And then stop complaining about those greengrocers apostrophes.