My experiences: in 2009 was online when fares were updated - got $79 each way, Pittsburgh to MCO (for an early December flight). Later that same day some of the flights were up to $120 each way, including ours; during the later weeks some of those dropped back, and the $79 fare was still available for one or two flights. Ours never did drop back down.
This year, going in October, so can't book yet, but have been watching the fares closely. When the last update occurred, and I again was online the day they extended the booking period, fares were pretty much $120 each way across the board. A couple of weeks later they fell to $95 each way and the majority of those remain there (even through the summer, up to August 8, the last booking date currently available). I continue to monitor the fares, watching for any sort of pattern.
My advice, which may be too late for you if you plan to book Sunday when the schedule is advanced, is to watch your flights before the schedule changes. That might provide a clue as to their movement, but even then you are at the mercy of supply/demand, the time of the year you are flying, fuel prices, route cuts, etc.
The golden rule seems to be: if you find a fare you can live with, book it.