Hey, @Kosmonaut: Question for you, which, if you don't have a ready answer for, I may ask as a general question on the site proper:
Question tags: Do they always require a question mark? I see them both ways quite a bit, by competent writers whose prose I respect. In speech, question tags that are simply extensions of a declarative statement seem not to require a question mark. Others that really do ask for clarification, seem to require one.