"Bill [Gates] doesn't really want to review your spec, he just wants to make sure you've got it under control. His standard M.O. is to ask harder and harder questions until you admit that you don't know, and then he can yell at you for being unprepared. Nobody was really sure what happens if you answer the hardest question he can come up with because it's never happened before."
Read the whole thing, it's an interesting look into Excel's weird date functions, Bill Gates and managing a software organization.