Grammar Friday - Prepositions at the End of a Sentence

So, we've all heard that we're not supposed to end a sentence with a preposition. Yet we all speak doing exactly that. Are we wrong?
Well, what does the Gregg Reference Manual say about it (section 1080 a-c, p. 347)?

Short questions and statements  frequently end with prepositions.

• What is this made of?
• Where did he come from?
• You have nothing to worry about.

What about you? Do you have any interesting grammar rules that you have to jump around in your writing? Or any special secrets that make navigating the English language easier?