as i've said before, i don't really think the vice presidential nomination matters all that much, except that if played right it can get the candidate a lot of positive media chatter. biden seems to have done that. and the more i read about this race knowing the biden nod, the more i see extra benefits of the nomination.
as mithras points out, if obama is elected (and dems maintain a majority in the senate--which is almost certainly going to happen), chris dodd will become chair of the foreign relations committee. that would be a really good thing, IMHO. in fact, i think dodd is better for the job that biden, mostly because i don't like biden's position on iraq. but with biden as veep, he's likely to abandon that position and start defending obama's iraq withdrawal without partition plan. an net gain all around!