This has been Obama's race to lose for a while now, and in a race that will come down to single percentage points in a number of swing states, there is a really important factor in the Biden choice that has gotten no coverage so far: The NRA HATES Biden.
So far firearm rights have been a non-issue in this campaign. Obama is sort-of anti, but hasn't made a big deal of it; McCain is sort of the reverse. But Biden... Biden has been near the top of the NRA's hate list for years, and his place on the ticket means the NRA will be pushing HARD for McCain.
That will be good for at least one, maybe two percentage points nationwide, and that may be the election.
I am personally trying to avoid emotional investment in this race; I am well and truly sick of the Republicans, but the idea of a Democratic President backed by substantial majorities in both houses of Congress (and those majorities WILL happen, regardless) scares me pretty badly too. I have been mostly just trying to get used to the idea of President Obama for good or ill, and now that is REALLY uncertain.
I SO wish we had a parliamentary government...