Yes there is a variable in conducting opinion polls where a pollster attempts to quantify support through a ratings response often 1-5, five being the highest but enthusiasm gaps in political polling only matters in down ticket races and or off-presidential election and or local elections/referendums when it predicts turnout in those races. PERIOD. You may read details about recent voting patterns going back to 1996 here, but this is the basic.
Self-identified partisan party registered voters vote in excess of a rate of 90% regardless of enthusiasm for their candidate or the enthusiasm to vote against the other party's candidate. 2008 89.6% of all registered voters actually cast a ballot, up from 88.5% in 2004, up from 2000 where 86.5% and up from 1996 82% registered voters actually voted. Enthusiasm can be measured in new and reactivated self-appointed partisan voter registrations with either inactive or disenfranchised voters, but 9/10 of registered voters will cast a vote regardless of enthusiasm.
Let me repeat, at the top of the ticket, especially Presidential elections, enthusiasm is a straw man bull-hockey meadow muffin, because partisans who are registered vote in excess of 90%. The question is the bad data regarding what is identified as inactive voters where people have moved out of state and registered in new states.
Now where enthusiasm or support can be measured is in independent or self-identified unaffiliated voters who are privately partisan in 29 states. Turnout among unaffiliated voters drop between 5 and 10% but this is also where the most inactive voters reside---meaning that this as much bad data than lazy voters.
So when you see a poll of registered voters like NBC and it says 49-44% it is closer to that than what they identify as likely to vote. My bet is that if you drill into their data it will discover that the largest lukewarm or maybe or possibly vote response will be in the unaffiliated or independent voter demographic.
I think the most important detail in the NBC poll is that 62% want major changes in the next four years....but what kind of change or what kind of result from which demographic?
The other variable in national polling for popular vote is the weight that Red states voting for Romney which is exceeding to 60% while in Blue States for Obama is around 55%. The reality is the vote in the battleground states.