Really really busy. They've got a significant amount of area and airspace (SFC-15000) and JAX is just one part of what they do. Lots of military, GA, overflight, and VFR stuff. From talking with friends there, developmentals get checked out on tower very easily and then radar can take an incredibly long time. For a while they had 6-day work weeks which I think subsided. Was also hard to transfer out due to staffing numbers.