May 10 is around when a lot of colleges start getting out, and so that kind of gets the summer "season" underway.
I'd use the farecast.com and kayak.com types to check the trends. I'd wait a month or so, and then look how things are going.
I've noticed that the lower buckets are being snatched up too. Looks like another summer of packed coach cabins for (some of) us! It was reported today that higher consumer spending raised the US economy's 4th quarter growth to 3.5%. Which translates into more tickets being bought too.