On one side we have what seems to be unenthused Dems. Signs of this are sizes of Obama rallies, lack of signs, anecdotes, massive losses in Democratic party registration across swing states. Real numbers also coming in from Ohio absentee ballot requests also seem to imply this.
On the other hand is the ABO crowd, Republicans, including estimated 41 million Tea Party members who would crawl over broken glass to vote Obama out. Many more might be lukewarm about Romney (but enthused about Ryan) but they want Obama out any way they can. Signs of this are bigger RR crowds, more signs, anecdotes, big increases in Republican registration e.g in Florida since 2008.
Turnout is key but I’d bet on the enthused crowd any day.