This is exactly the reason why:
HILLSBOROUGH COUNTY VS. FLORIDA
2000: R+3.10
2004: R+1.77
2008: D+4.30
2012: D+5.79
ORANGE COUNTY VS. FLORIDA
2000: D+2.05
2004: D+5.22
2008: D+15.81
2012: D+17.32
This would be a huge problem for Republicans if this trend continues, since both counties are getting pretty populated. It would mean Democrats have a 5 large county base when you include the South Florida counties, instead of just the three 3 down there.
Florida is probably not getting as democratic as some other states like Virginia and Colorado though. So it will probably remain super-competitive for a long time.
The whole state: estimates
2000 even
2004 +3
2008 +5
2012 +3
1976 was the last time Florida was to the left of the popular vote and before that 1948. It's not as red as it was in the 70's and 80's but no states are due to the huge landslides Republicans saw in those decades.