They are suppose to be building another one from Big Talbot Island to Fernandina Island sometime in the future, but will probably take 10 years years. The JTB trail is a nice 29 mile route. What makes it nice is that you can ride it 4 times and do a century for the most part without having to worry about cars and there are benches all along if you need a rest. The trees are really nice to help keep you cool when the heat and sun are really on. The only issue really is water although they do have a couple of place along the trail about 6 miles and 12 from the east trail head that I believe have water, although I've never stopped at either to check. If I do a second run, I usually bring water with me to refill my bottles. Just make sure you don't get stuck out there at night, issues with kids and vandalism to cars has been a problem in the past. If you want to meet up out there sometime, PM me and will get together.
Another good point is that you can use it as a staging ground to do some longish rides to the Okefenokee swamp that is about a 102 mile round trip. There are quite a few maps at the North Florida Bicycle Club that use the trail as part of the ride. Here a link.
http://www.nfbc.us/Rides/Maps/tabid/109/Default.aspx