I'm normally loathe to play the "this poll shows that X voting block is a crucial battleground" game because just about any poll, including a poll of people's favorite breakfast cereals, can be overlaid on a two-way presidential race and made to seem significant.
However, I do think that this particular poll concerning overall voter attitudes gives a good idea of what the task is for Obama in this race.
Basically, 64% of people are concerned that McCain will pursue policies similar to Bush's. That's a large enough chunk that you have to figure things are looking good for Obama. However, when you break it out into "very concerned" and "somewhat concerned," the "very concerned" number is under 50%.
Obama's campaign should be focused more or less exclusively on getting those 17% of people who are "somewhat concerned" over into the "very concerned" category.
The nice part about this strategy tactically is that these people are almost by definition predisposed to the idea that McCain is like Bush. After all, they are "somewhat concerned" about it already. A big McSamey ad-bomb should sway at least a few of them who might be wondering if their concerns are enough to push them to vote for Obama.