Actually, go ahead and ignore what I said in the last post about book earlier not necessarily being better. Cheap Air posts a different article the same day saying that the other article doesn't always hold true:
Flights to Florida for Spring Break are a great example. If you want to travel on weekends, especially, reasonably priced seats on those flights can be extremely hard to come by. Also, flights to Europe for the summer. In that case, we actually found that the best time to buy was 319 days in advance! And the best day to buy domestic flights for both the Thanksgiving and Christmas periods was June 4th, 5 months before Thanksgiving and 6 months before Christmas.
So, after all that, it pretty much leaves me further in the dark about when the best time to book flights are.