I post way too often about things like this, but I find English language, etymology, and the origin of idioms so very interesting. So. My tidbits to share today:

"Bated breath" is *not* correctly spelled "baited breath." This is because "bated" is actually an abbreviated form of "abated," which is why bated breath implies breathlessness.

"Just deserts" is *not* correctly spelled "just desserts." Yes, it's pronounced like "desserts," but the origin of the word is not the food but a kind of slang for "things deserved"---"deserts."

So there you have it. Lovely bits of idiom correctness courtesy of The Phrase Finder! (And if you're feeling idiom-geeky and rather ambitious, check out the entry on "beg the question.")