1. I think that twice within the last week I've heard someone describe someone else as being "Smart as a whip." Which sounds like it would be a put-down, but they meant it as a compliment. I never knew whips were so smart. I'm pretty sure they meant to say "quick as a whip," which makes much more sense, and is also a way of saying that somebody is smart.
As an aside, I sometimes like to say that someone is "sharp as a whip, quick as a tack," which is funny because I am intentionally switching the adjectives for humorous effect.
2. "The proof is in the pudding." Why do people say this so often? Don't they know it makes absolutely no sense? There's no proof in the pudding. Why would the proof be in the pudding? J.I. Packer has surmised that the original saying was once "The proof of the pudding is in the eating." This makes a little bit more sense, although I admit that I'm still not sure exactly when it would be appropriate. Unless I were having a very specialized debate about the existence of pudding.