David Paul Kuhn provides 5 reasons that McCain and Republicans have surged in the polls. I think his reasons are actually a bi product of the root cause, which is that Bush Derangement Syndrome is a spent force and what is left of it has been unwisely redirected into Palin Derangement Syndrome.
Ever since Bush was elected, a small portion of the population has viscerally hated him and wanted him destroyed politically. For the first several years of Bush terms, these Bush haters were constantly thwarted. However, starting around 2005, events started mounting making the Bush Derangement Syndrome more palatable to the general public. In response to this, Bush did nothing (he provided no leadership, and provided no counter arguments that his supporters could rally behind).
Some of his supporters tried to rally to his defense. However, anyone who rallied to his defense would be subjected to insults questioning their intelligence and mocked for being brain washed kool aid drinkers. It takes an immense amount of fortitude to withstand these constant insults for having the audacity to support Bush. Considering that not even Bush was engaged in the "battle" for hearts and minds in America, most of his supporters decided standing up for Bush was not worth it.
Consequently, the Bush haters won. The battle is over. The Bush haters had nearly 2 years to gloat over that victory. However, that battle finally came to and end at the Republican National Convention. Bush is destroyed politically, and everyone has accepted it. The fight now is for the future, and McCain is providing the good leadership for the Republican troops, who are rallying around him and showing independents and Democrats that they can support a Republican without needing the fortitude it takes to defend Bush.
The Bush haters can continue to try to destroy Bush politically, but at this point, to most Americans it just come across at gloating over a victory that has already been won and is not worth talking about anymore. Some are redirecting their fury to Palin, but those efforts are back firing and giving Republicans another strong figure to rally around who seems very willing to again provide leadership in "battle" for the hearts and minds of the American people.
Update: This Onion video mocks the phenomenon of which I speak.