Yeah, polling is definitely not exact and it is WAY to early to tell what will happen. But if you look at the movement in a single given poll over time, you can get a good idea of trending, even if it doesn't give you an accurate absolute reading. If you get on your scale every day, and over the course of the year it goes from 185 to 200, you might say, "That scale is off! I'm not fat!" That might be true, but you are getting fatter. Same deal here --- the change in the polling does not guarantee Obama will win any given state that CNN has colored blue, but it's pretty safe to say that if they are switching states blue, that indicates the direction things are trending at this point.

Still, you are right that it is too early to say how these trends might bear out over the months to go. My feeling is that Obama is gaining momentum and McCain is floundering, but we will see if he can gain his footing and catch up.