Well, I just called last week for Gay Day/Star Wars weekend and was able to book a DVC villa. I tend to wait to the last minute too often. I've been lucky.
If I were going to book a vacation that included airfare, then I'd definitely start close to a year before. Waiting is too nerve wracking and not cost effective. I like to try and find a nice hotel wherever it is that we are going and that takes time and research.