Moved down here from Boston 3 years ago and we really like it. You have 3 "seasons" here for a change of pace and the property values are reasonable (although like most places in FL have increased over the past few years.)
A home on the intracostal runs under 400K and the schools aren't bad relative to the rest of the state (although they don't compare to the Northeast so private school may still be necessary.)
Some people say that it might as well be Southern GA, and in some case it may be true, but if you live on the Southside, Ponte Vedra, or the Beaches, you would be in anywhere USA (Northeast, Midwest, etc.)
The biggest drawback is the relative lack of cultural activities compared to a big city.
The Jags are the biggest thing here, and the games are great fun even if you aren't a football fanatic.
Overall, the quality of life is excellent, no income tax, reasonable property tax, (4K on a 300K home), great weather, and a good family atmosphere.