Field, Rivertown is a CDD, but the builders still pay impact fees and residents still pay property taxes to the county.
As for the busting at the seems comment, kind of irresponsible to say when Nocatee and Durbin Crossing are blowing it out of the water. Nocatee is miles and miles ahead of Rivertown right now and seems to be growing steadily. My brother in law is a builder there and says they are really busy with no slowing in site.
That said, I do like the Old Florida feel that St. Joe has gone for with RiverTown. They have also attempted to stay true to TND principles, but I have reason to believe the lack of a market is going to make them modify some of their neighborhood plans.