One other thing to consider, if you're staying in (or near) Key West is the length of the drive from Key West to any of the inland airports (either Miami or Fort Lauderdale). On our trip, we spent 4 days down there and we spent the first night in Key Largo and the last 2 in Key West. We wanted to get home pretty early the day that we were leaving (it was the 4th of July and we wanted to catch the local fireworks at home) so we booked a 10:30 or 11:00am flight out of Fort Lauderdale and, when we did this, we COMPLETELY forgot how long of a drive it was from Key West back to the airport.

I remember it taking a good solid 3-4 hours (depending on traffic and your willingness to risk a speeding ticket) to make the drive, so we ended up having to get up at 3:30-4:00am and drive pretty aggressively in order to make sure that we made our flight home. Just something (else) to think about...