One obvious hazard of picking a veteran like Joe Biden is that it complicates Barack Obama's promise to "change the culture of Washington." The campaign, of course, has thought of that, too. And just now, on MSNBC's Morning Joe, Obama spokesperson Linda Douglass gave their answer: "He's not of Washington, he goes home to Delaware every night." From there, she described Biden's working-class roots and feel for the average American--contrasting his background, later, with the background of Mitt Romney, whom the hosts had suggested might end up as McCain's counterpart on the Republican ticket.
Substantively, that makes sense to me. As I argue in my article on the selection today, the fact that Biden is the least wealthy member of the Senate despite being one of its longest serving members speaks well of his virtue. And the blue-collar image is absolutely real.
That said, I imagine Biden's selection will indeed make it harder to run against Washington per se. And that's ok with me. I've often thought that the Obama campaign had become too focused on changing the culture of politics, rather than improving people's lives. If picking Biden forces them to do more of the latter, that's probably a good thing.
One other note: She noted that Biden is "never at a loss for words" and then hyped his ability to be a strong voice within the administration; she also stressed that he and Obama didn't necessary agree on every single issue. This, I presume, is how they'll handle past quotes of Biden criticizing Obama.