Dear, Gentle Readers,
Madame L has found what seems to be the definitive article on comma use.
Some examples from the article:
My son, John, is awesome. (If you have just one son.)
But withhold the comma if not unique:
My son John is awesome. (If you have more than one son.)
Enjoy, but beware: There's a mistake in it.
Madame L was writing about commas because as an editor and teacher she noted that students often followed the "sound rule: for commas: If you hear a pause when you say the sentence aloud, you should insert a comma in the written sentence.
This "rule" is bogus. The only way to get commas right, for sure, is to follow the grammatical rules, and the best way to learn them is not by memorization but by reading a lot of correctly edited writing. (In other words, reading a lot of stuff on the Internet won't help.)
Here's another great article with more on grammar and punctuation.