Nice piece published today by Andrew Sullivan: http://andrewsullivan.thedailybeast.com/...
Some tidbits below the fold:
To wit: in 2008, Gallup missed the margin of victory for Obama by six points. That's a huge discrepancy. And that time it was in Obama's favor: they predicted a landslide double-digit 11 point victory, when it was only 7 percent. But they were dead-on in 2004; and now they are claiming that the demographic make-up of this year's electorate is almost exactly the same as they measured 2008. So with the same turn-out in terms of race, age, gender etc. they are predicting this time a Romney victory over Obama of five points. From 2008 to 2012, Gallup believes that Obama has lost 17 points to the Republican challenger.
Gallup weights its sample for party identification. They say their model for 2012, with the same demographics as 2008, is 36 percent Republican; 35 percent Democrat; and 29 percent Independent. The poll of 705 other polls shows party identification as 29 percent Republican; 36 percent Democrat; and 31 percent Independent. What has happened since the summer is a sharp drop in the "Independent" category - giving gains to Democrats and Republicans pretty evenly, with the Democrats gaining a tiny bit more.
Go check out his page. The graphs he includes show just how "skewed" Rasmussen and Gallup are versus the rest of the pollsters.