Well, I can say I havent quite done it two year in advance. We stayed at the Swan in 2002. I wanted to make sure I received the teacher rate so I called in July of 2001, a full year in advance. I felt kind of funny calling that far in advance, but the more I read on these boards, its not so uncommon.
I think its a great idea. I know if it was me, I wouldnt be able to save for 2 full years. Im two spend thrifty. We tend to find the money somehow before our trip and have a fabulous time.
Good luck with your planning and saving!