Most pundits missed the best part of the new arrangement, though, until the joint appearance from Springfield, IL, when Biden began speaking: Biden provides chops.
He is the attack dog (or, these days, does one spell that "dawg?" I'll have to ask my 20-something year-old housemate when he gets back to town...). Biden will be Bad Cop to Obama's Good Cop. He came out swinging, which I think is a good thing, both for the ticket and, oddly, for Biden.
From the standpoint of the ticket, Obama can make the case for their own ticket, while Biden can keep reminding people why the other side is flawed every which way.
From Biden's standpoint, this can only be a free ticket to blissville for the next two and a half months: the man likes to rail against bullshit, and, with a ticket position assured, he can stop selling Dems and start selling it to everyone else. He seems to thrive in a campaign setting, which adds energy to his talent in the Senate, which is in-your-face debate and boldly calling bullshit for what it is ("Don't listen to Rumsfeld! He doesn't know what the Hell he's talking about!" he once told someone in a committee hearing).
This, in turn, absolves Obama from getting his own hands dirty. He can remain above the fray, doing what HE does best. Call it what you will, "broadcasting optimism" or "blowing rainbows up people's asses," he does it best when not also having to get dirty.
In any case, I think this is likely the best ticket possible for the Democrats in 2008. I am looking forward to the debates...