It's true about Florida. Drive up the east coast, once you drive though Palm Beach county (heading north) and into Martin county, you'd swear you were in Georgia. It's a sudden change. Even environmental. Since zone 10 (topical) ends somewhere near on the border of Palm Beach and in Martin counties.
Personally i would hardly consider Tampa and Orlando as Dixie. Slightly conservative? certainly. Though not Southern and more an odd mish-mash of liberal and conservative, mostly pro-development, but with an odd pro-environmental strain in the Tampa area. Gainesville, FL is an odd duck miniature city-state: half-Southern, half-hippie values, similar to Athens, GA.
Yeah the west coast of Florida has always been a little hard to predict. Another good example is Sarasota - which is 1/3 southern, 1/3 hippe and a 1/3 retired.
But in the east, generally, once you are in Martin and up - it's southern. That's doesn't mean there aren't nice towns up the coast - Stuart, Verio, Coco Beach. Daytona, etc etc.
Edit: Correction. Zone 10/9 are expanding. Which makes sense considering global warming. See http://www.garden.bsewall.com/topics/hardiness/maps.htm