I'm of two minds about this. Biden's home state, Delaware, has only 3 electoral votes, and was pretty much a lock anyway. And he has a tendency to say stupid things, including stupid things about Barack Obama (remember the "clean and articulate" thing?).
On the other hand, he's a great attack dog. His line about Rudy Giuliani's sentence formation ("a noun, a verb, and 9/11") was classic. And he brings a lot of experience to the ticket, including on foreign policy, which should either reassure voters nervous about Obama's lack of experience, or draw attention to it.
One other thing of interest:
He was ranked 99th out of 100 senators in personal wealth, and owns only one house. This provides a great contrast to John "I don't know how many houses I own" McCain, and whoever his VP will end up being (lots of people are thinking Romney, whose family wealth may add up to some $500 million). It'll take a shitload of cognitive dissonance for the Republicans to keep pushing this elitist nonsense.
PS: Why the hell did Obama release this news on a Saturday? Isn't this the worst possible time in the news cycle? I don't get it.