How far out do you book?

[FreeTime]

When I called DCL they explained that the further out that you book the cheaper it will be. I booked with a travel agent for next May. I decided to call today to see how much cheaper it would be for the following year for the same time thinking if it was significantly cheaper that we could wait another year. Well it was almost $2000 more for 2006. How do the DCL prices work?
Thanks!