We're going from BOS to MCO and back on Song the last two weeks of July. I booked the tix at the 330 day window and with taxes paid $143 roundtrip. I found out in December that we need to add one more person to our party and the best fares are in the $165 range if we are flexible and just over $200 if they fly on our flights. When I look at seat availability the planes are still wide open, so I'm going to wait to see if a fare sale comes up between now and May before booking. I'll keep an eye on seat availability too, because if the planes get pretty full Song won't discount at all from that point forward.
I've found that JetBlue can often provide a cheaper flight at the same leave/arrive times as Song so I always cross shop them for flights. Just last week, my daughter flew back to college in the Orlando area on Friday the 7th and Song wanted $199 one way for all Friday flights (and $65 for Saturday flights, but my daughter needed to be back by Friday night) for planes that were pretty empty. JetBlue had fares from $69 to $99 available depending on flight on Friday, so we sent her via JetBlue.
Good luck with your flight shopping. I'd suggest setting some flight alerts on MyYahoo and joining Orbitz to let you know when fare sales are announced.