You know why punctuation is such a thorn in our sides? (Besides the fact that it seems to be engulfed in an arbitrary set of really picky rules, I mean.) This is why: when you get it right, no one (except your English teacher) notices, and when you get it wrong, people point it out.
OK, not a lot of people. Mostly, people like me. But (stomping my foot) it matters!
For example....Christmas cards. (I know it's a bit disingenuous to critique holiday greetings, but goodness - such a broad target!)
Folks, "Merry Christmas from The Smith's" is wrong. The Smiths are the Smiths. Putting in an apostrophe is fine if you're referring to the Smiths' dog, but if you refer to the Smith's dog, I'm going to have to assume you mean the BLACKsmith's canine. Get it? If the dog belongs to the Smith family, also known as the Smiths, it's the Smiths' dog. Ergo, it's the Smiths' greetings. And I'm sure they were merrier than this...