I think they could lose Florida and still have a comfortable shot at winning, as long as they don't lose PA. However, if they've lost Ohio, then they've already lost FL and PA, and the game will be pretty much over.
I just can't see them losing such huge states that are usually good indicators of a 50/50 country (IE: Florida, Ohio) and then have western states that went for George Bush NOT go for John McCain.
That's why I think they can lose Florida but still carry PA and OH. They are all close to the center as far as voter turnout. I think in this current match-up, Ohio is leaning more Dem, PA is on the balance, and Florida is leaning Rep. So as long as the Dems carry OH and PA, they can afford to lose FL if they pick up something in the Great Lakes or midwest areas. However, they can carry OH and still lose the election if the Reps can claim PA. And of course, if the Reps get OH, it's all over.