I was born and raised in Jacksonville. There's a lot of truth in this thread, but there's some good to go along with the bad.
It's true that Jacksonville is a very redneck town. If there were a competition for "most white trash" city in the country, Jacksonville is easily in the top three. And it doesn't really have the southern charm of other, similar cities to offset its more colorful inhabitants. On top of that, the crime rate is higher than similar-sized cities.
As for the economy, yeah, CSX is a big player in town, and so is the Navy. The port doesn't just export cars, it's also a major supply terminal for the Marines. But there are other big industries in town. It's also got two big paper mills (which used to stink to high heaven when I was a kid, but they managed to clean up their act somehow), and Anheuser-Busch has a huge brewery there, too.
It's not a bad place to live. Property values are pretty low, thanks to low population density. The cost of living is below the national average. It doesn't suffer from constant hurricane threats like other coastal cities in Florida. There are lots of prosperous communities situated away from the redneck elements. There are plenty of museums, musical venues and other things to do.
I think Jacksonville suffers from an image problem. It just isn't very glamorous - there's no real tourism to speak of, unless you're a golfer. The beaches aren't pretty at all, especially compared to other Florida beaches. No one wants to take a vacation to Jacksonville, after all.
Except maybe Ash Williams.