The worst, though, is when a comment tells you the valid input range, but it's wrong, because someone later changed the code and didn't update the comment. While this doesn't happen frequently, I've gotten bit by it enough that I will generally at least take a cursory look over the function body to verify that the comment is still correct.

I wouldn't say this makes the comment useless, but it does reduce the usefulness. And this might end up biting someone who has decided to trust the comments.