I just (an hour ago) booked a ding fare (3 people from Buffalo to Orlando) in May for $331.80 total. This fare was available from March through May - very flexible. I think they key is to be quick and hop on a ding as soon as you notice it. I did book my stay at WDW a few weeks ago and I made sure that my arrival and departure did not occur on a weekend - as weekends can tend to have more limited availability.
Somewhat flexible, like the previous poster said there is less available on weekends. I booked ISP-MCO today $44 each way, I'm flying Wed and Tue. i could have flown the weekend, but we would have had to fly down late and come home early.