As someone who DID quit my job and move to the Keys, I can tell you that anyone considering doing so should read this first. There's a lot of silliness thrown in, but hey, there's a lot of silliness in the Keys. Enjoy that part, but take the advice they give very seriously - as a "local" I can tell you it's all true. I think these guys hit on all the important issues, though perhaps too lightly in some cases. The only thing I'd add is that the job market is very limited (the majority is either hospitality/tourism related or local government), so secure a job before you go quitting the one you have.
The Keys are more expensive than wherever you live now, unless you're in NYC or LA. The rule of thumb I've used is to take what you currently pay for a mortgage and double it to rent a place half the size and with a tenth the storage space - and that's if you're lucky. All the necessities of life are more expensive - gas, groceries, utilities, etc. - so be prepared for that (the Keys don't export anything, so when a truck brings supplies in, they have a 100+ mile return trip with nothing to show for it...prices go up accordingly). But if you want to live in paradise, so you will accept that. For as long as you can afford to, that is. Too many of my friends ended up working two (or more) jobs just to get by, and then not being able to enjoy the island life you moved there for - they didn't stay long. If you want to stay, and you don't have a trust fund backing you, your only option is to reduce your standard of living requirements and be happy doing so. After all, your quality of life will go up exponentially! If you can shed your desire for material goods, be flexible on housing and transportation, and are willing to do whatever job happens to be available, you'll do just fine, and you will love the island life.
You know you've assimilated when you have more swimsuits than dress suits, "formal attire" means your "good" flip-flops, "the good dishes" are any you don't toss after using, and you start planning your next Fantasy Fest costume as soon as your hangover from the last Fantasy Fest wears off. It's a wonderful, crazy world.