Others will have a lot more to say about Barack Obama's choice of Biden than I do. For now, I will make just three brief points. First, as with most Veep picks, we should focus more on Biden's potential as a possible future president than on his possible impact on this race. As of today, Biden has become a leading contender for the Democratic nomination in 2012 (should Obama be defeated this year) or 2016 (if Obama prevails in 2008).
Second, it seems to me that Obama's choice of Biden reflects confidence among Democrats that they are going to win this year and don't need any boost from the VP pick to do so. Biden is not particularly charismatic, won't enable the Democrats to win any states they wouldn't take otherwise (Delaware is a Democratic lock anyway), and is just as liberal as Obama (therefore with little ability to attract moderates). Virtually his only political assets are his being a white male (which might perhaps reassure some traditionalists or relatively mild racists), and his having more political experience than Obama. There are many candidates that Obama could have chosen that would have brought greater electoral advantage, such as Senator Evan Bayh of Indiana (a well-respected moderate who is more charismatic than Biden and might have put a traditionally Republican state in play).
Third, the choice of another very liberal senator as veep is one more sign that Obama has little intention of moving to the center anymore than is absolutely necessary to win the election. The selection of a prominent moderate such as Bayh or former Iowa governor Tom Vilsack might have been of some small reassurance to people like myself who fear a vast expansion of government should Obama win the election and get the chance to govern with a strong Democratic majority in Congress.
In fairness, even if Obama had picked a moderate, I would still put more faith in the power of divided government to stem the growth of the state than in the potential influence of a moderate veep. This year, the only hope for divided government is a victory by McCain, no matter how flawed he is in other respects. However, not all libertarians and pro-limited government conservatives are as committed to that view as I am. Some of them are supporting Obama or are at least open to doing so. It is perhaps of some note that Obama decided to deny us even the modest hope that could have created by picking a moderate veep who could have been expected to press for centrist policies.