A diary about the RAND Tracking poll is currently at the top of the rec list. Over the course of a few days, Obama has gone from a two-point spread to a six-point spread. Every day, Rand also posts a demographic breakdown by a chosen characteristic that varies from day to day. Today they are focusing on household income. You can see the charts here. [If somebody can tell me how to embed, I will].
While preferences have been relatively steady among individuals in households with $50,000 a year or higher, the "bumps" have largely come from the under $50k respondents.
They were almost exclusively responsible for the "47%" bump -- the story broke on 9/17. By 9/26, Romney support in this group has plummeted to 36%, with Obama being about 20-points higher.
Over the next few weeks, perhaps due to reversion to the mean, and assisted by the re-emergence of Moderate Mitt (unchallenged by the President in round 1 of the debates), the spread has shrunk to 11 points, hitting a minimum on 10/19. In the five days since--probably reflecting the full effects of debate 2, and helped along by debate 3, the spread is once again near 20%.
Internals are "noisy", as pundits will tell us, but the 50,000 and under group is about half of the country, and hopefully, at least half of the sample, which would mean about 1500 people. [You can see that the noise in this group is much lower than in the $50-$75k group]. Also, the true "panel" design -- querying the same people vs. new samples everyday, as other trackers do, reduces the noise considerably. In fact, despite its quirky design in other areas, I would argue that the RAND experiment is hands-down the best source for tracking these trends.
The low income group will include disadvantaged minorities and young people, so its hard to conclude that this is strictly an income effect. But the good new is that, yes, people do know how to vote according to their economic interests.
The bad news: We all know lower income voters are the least likely to show up at the polls. Early voting and the ground game are still critical for a decisive win this year.