In my opinion, some of the 7 questions that Gallup (and other pollsters) ask respondents in order to get their likely voter results seem... well, questionable - at least in 2012.
The calculation of likely voters is based on registered voters' responses to a seven-question series that -- with some revisions along the way -- Gallup has used since 1952 to calculate voters' likelihood of voting. In some years, such as 2008, there was only a marginal difference between the vote choices of registered voters and likely voters. In others, such as 1996, there was a much more substantial difference.... At this point, Romney voters are somewhat more likely to respond that they will definitely vote, that they have thought a lot about the election, and that they are more familiar with where people in their local area vote. These attitudes indicate that Romney at this juncture will benefit from higher turnout on Election Day among his supporters than will Obama.
Gallup is using the idea that if a voter "thinks a lot about an election" that they are more likely to vote for the candidate they're currently supporting.
That may not make sense in 2012. There may be reason to believe that in this peculiar election cycle, a person who's really thinking a lot about the election is that would-be Romney supporter who's just not that into the guy. In a more typical election, like with GWB, the question might be more productive, ie it would merely reflect an engaged voter.
It would seem to me that someone who's thought a lot about this election wouldn't necessarily be such a sure thing. It doesn't sound like an Obama supporter. It sounds like someone who isn't all that thrilled with Romney, who's been watching closely to see what kind of man he really is (hint, not a very good one).
Obama supporters don't really have to think a lot about this election specifically. We'll be voting for him come what may.
Also, with mail in voting and given the nature of liberals, the question on knowing where people in your neighborhood vote also seems less likely to have an impact as in the past, in my opinion.
And finally, first time voters (ie young voters, some well into their 20's, and immigrants) can't really answer some of these questions in a way that would suggest they will vote, so they're probably automatically dropped out of the equation to some degree (see questions 3 and 4 below).
I couldn't find the 7 questions at Gallup, but USA Today also has 7 and they're probably very similar if not identical.
1. How much thought have you given to the upcoming election for president? Quite a lot. Only a little.
2. Do you happen to know where people who live in your neighborhood go to vote? Yes. No.
3. Have you ever voted in your precinct or election district? Yes. No.
4. How often would you say you vote? Always. Nearly always. Part of the time. Seldom.
5. Do you plan to vote in the presidential election this November? Yes. No.
6. Are you now registered to vote in your precinct or election district? Yes. No.
7. If "1" represents someone who will definitely not vote, and "10" represents someone who definitely will vote, where on this scale would you place yourself? 1-10.
In my personal opinion, I think the likely voter questionnaire is dated, and quite possibly does a disservice to the polling in 2012 - of course, as usual, in favor of Republicans.