I remember. I've never run a race there but presume not all of these are mega-events. Some are clearly trail races and would have limited numbers (500-750 maybe). I'd guess at least a few of these marathons must fill up for organizers to take risk by adding more races. I think it would be great if all these races could generate enough participants to survive, but I'm skeptical.
On a related note, I was surprised to read that 2010 will be the last year for the Gasparilla Marathon. I was even more surprised that they are still keeping the half marathon, along with their traditional 5 and 15K races on Saturday. They cite costs to the city (it's a co-sponsor) and the current economic climate as the reason to cut the marathon. Only time will tell if they reverse the decision.
Given the growth in half marathons, I'd be looking to see if some marathons just cut their distance or find ways to offer both.