How to use apostrophes, for God's sake

The use of apostrophes in the English language is often entirely woeful. I think people failed to grasp the concept when young, and now, when presented with a "should I, shouldn't I?" dilemma, they panic and start throwing them around like they're confetti.

They're not that bloody hard to learn. I'm going to tell you how to use them. Two little rules, and one addendum. That's all.

1: Apostrophes should NEVER be used to denote plurals.

No, not if the word ends in a vowel. No, not if it's an abbreviation*. NEVER.

Examples of how to do this:
     I ate three burritos.
     I ate seven tamales.
     DVDs for sale.
     The 1920s.

2: Apostrophes are ONLY to denote either a) one or more missing letters, or b) possession.

Examples of missing letter:
     Didn't - short for "did not".
     It's - short for "it is".
     That's - short for "that is".
     You're - short for "you are".
     Who's - short for "who is".
     The '90s - short for "1990s". [OK it's a missing number - same principle though.]

Example of possession:
     The cat's basket.

If it's a plural and a possessive, then you move the apostrophe to the end of the word. Example:
     The dogs' bones. [The bones belong to the dogs.]

If the plural doesn't end in a letter S, then you do it just like the singular:
     The children's playground. [The playground belongs to the children.]

Addendum:

Treat the possessives "its" and "whose" like you would "his" or "hers".

Examples:
     See that car? I like its color. [The color belongs to the car]
     That is the man whose fish died.

This Public Service Announcement has been brought to you by Jim's patronising nitpick factory. Thank you.

P.S. I'm proud to say that the worst apostrophe abuse I've ever seen ended up in on page seven of Lynne Truss's excellent book Eats, Shoots & Leaves: The Zero Tolerance Approach to Punctuation, which I command you to buy and read. Don't argue with me, just get it.

*This is a debatable stylistic point, and, in my opinion, is what caused all the confusion in the first place. So shut up.