The apostrophe (2)

In a previous post I mentioned the so-called "Greengrocer's apostrophe" (which could equally be written Greengrocers' apostrophe). It is perhaps unfair to single out greengrocers, although maybe because of all the hand-written notices they have to do, they have more opportunity to fall into the trap than others, but this is the error of putting an apostrophe before a plural "s" - as in a pound of apple's, a box of toy's, a row of house's and so on. The general rule is that apostrophes should never be used to indicate plurality - not even for abbreviations, so it should be CDs, not CD's for example. However, I would plead for a possible exception for individual letters and numbers - I would tend to write "Mind your P's and Q's" rather than "Ps and Qs", and certainly "how many r's are there in embarrass?" would to my eye look very peculiar without the apostrophe. Mind you, at the other extreme, there are those who would argue that the apostrophe is for the most part unnecessary - if I wrote Im sure youll understand me, I'm sure you'll understand me, if you get my drift. Certainly George Bernard Shaw was one of those who would have done away with it, as he would have done away with much of the peculiarities of English spelling and writing. There's a story about GBS which I'll save for another time.