There’s been some discussion of the idea that poll results have to be adjusted for party identification. In general, party ID is pretty stable over time. Vote preference varies a lot more. For a small amount of data on this, see Figures 1 and 10 of our 1993 paper.

You can adjust surveys by smoothing out party ID to get more stable
estimates over time, as we showed in this 2001 paper.

But I don’t know anything in particular about what’s going on in 2008.

I can see why political operatives want to look at these daily polls
but these horse-race numbers seem pretty irrelevant to me. Wherever
the polls stand, both parties have to go all out between now and the
election, both parties have to campaign in the swing states, to take
their best shots, etc. This is all true whether McCain is up by 5 or
Obama is up by 5.