My standard advice with Southwest is to buy the legacy ticket if it's a deep discount on a peak flight that's bound to sell out (e.g., Friday or Sunday evening). Southwest is stingy with deep discounts on peak flights, and apparently JetBlue is doing something similar.
Good advice - I wasn't expecting JB to be generous, just not blatantly greedy.
Frankly, after several days of extensive searching of flights for our 2/08 trip, outside of ridiculous connecting itineraries (ergo, White Plains, NY to Orlando via Detroit on Continental) there aren't (as I expected) really any truly deep discounts on legacy Fri/Sun flights, just nominal ones.
But I'm very quickly heading towards grabbing one of those. The "crunch decision point" will come tomorrow, for that's when the 330 day window hits our targeted return date (Sunday 02/24/08). If I'm going to buy a legacy ticket, it will be then, because the price isn't going to get any lower.