Apostrophe catastrophe

Went to town today and stopped at my favourite coffee shop -- hint: no lattes on offer there -- and found they have a new feature. Yessir, Vince has joined the wired world and is now offering a wi-fi section "for the convenience of our customer's". Sic.

Why "sic"? Because "customer's" is the possessive form of the noun "customer". I was left wondering...the (one) customer's what? The customer's cat? The customer's maiden aunt?

It's not Vince's fault. Misuse of apostrophes is everywhere these days, even in the media and the sign-painting community. I'm not talking about the endemic confusion of "its" and "it's"*, but such egregious errors as "It pay's to go Peugeot" and signs indicating that a cottage belongs to "the Smith's".

For those who went to school after "child-centred education" took hold, Walt presents the rules...

1. Use an apostrophe to indicate possession.
a) With nouns (both singular and plural) that do not end with the letter s, add an apostrophe and s. Canada's climate consists of nine months of winter and three months of bad skiing.

b) With plural nouns that end with s, add only an apostrophe. Flight attendants' duties include telling passengers to stay in their seats.

c) With singular nouns that end with s, add either the apostrophe alone or both the apostrophe and s, depending on which authority you choose to follow. William Strunk says you should always add 's, regardless of the final consonant. Thus, the witness's testimony.
An exception might be made for proper names ending in s: Jesus' robe, Dickens' novels, but certainly not Dicken's novels (because the author's name is Dickens, not Dicken)!

d) If possession is common to two or more individuals, only the last name takes the apostrophe: Bill and Ted's Excellent Adventure.
But if possession is not common, make each noun possessive: men's, women's and children's wear.

2. Use an apostophe in contractions to indicate omission of letters or numbers. Summer of `42 (not Summer of 42), can't, won't, he's, they're (for they are, not their or there!), you're (for you are, not your!!!), isn't, it's.

* Here's an easy way to remember the distinction between it's (the contraction) and its (possessive). It's raining outside so the dog went into its kennel.

3. Use an apostrophe with nouns that are followed by a gerund. Don't bother looking up "gerund". Here's an example: Walt's overeating led to three days of indigestion.

4. English being English, there are a couple of "special cases".
a) to form plurals of abbreviations that have periods: Ph.D.'s
b) with letters, where addition of s alone would be confusing: Mind your p's and q's!

All of which is fine, but begs the question: does anyone care any more? Perhaps not, but if you're writing, there's no harm in appearing to be literate, but great potential harm in the opposite. Think résumés...not résumé's.