Yes, it is perhaps the oldest cliche in politics to say that everything is riding on turnout. But take a look at the data for Georgia and Missouri in the latest TIME/CNN poll. In both states, McCain holds a narrow lead among “likely” voters (those who traditionally vote), but Obama leads among registered (the kind of result you get if turnout is huge).
UPDATE: (And h/t Jim Poniewozik, for calling this to my attention.) Might the above-mentioned poll explain why McCain doubled his ad units in Georgia yesterday?