I wrote one very nasty post about Joe Biden last fall, but if the scuttlebutt is correct and he's Obama's VP choice (and, yeah, who the hell really knows?), I get it and I think it's a fairly smart move.
Biden has become a gray eminence, but he's still vigorous, and his long suit is foreign policy -- those are the obvious reasons he might be the pick. But beyond that, it may be dawning on the Obama team that the McCain campaign is going to be even nastier than the ones run directly by Rove for George W. Bush; under those circumstances, you really want a guy who gets lippy on a regular basis. One of the cringeworthy moments of the '04 campaign was the VP debate -- Edwards never laid a glove on Cheney, and he never even seemed to try. From this op-ed, say, or from Biden's classic "a noun, a verb, and 9/11" swipe at Giuliani, you know Biden will hit back.
One lesser-known detail: Biden was the prime mover behind the Violence Against Women Act. For a lot of people that's going to seem like small beer compared to Hillary on the ticket, but it's not nothing. (Biden has been married to the same woman for more than thirty years, by the way; the marriage took place five years after his first wife died in a car accident.)
I don't know how Biden would match up against Tim Pawlenty, say, or Tom Ridge, but it's always seemed to me that McCain isn't going to have a running mate so much as an entourage (a posse? a Rat Pack?) -- the running mate may never be as close to him as his buds Joe Lieberman and Lindsey Graham, and they're going to do a lot of his dirty work. The VP choice may have to be the bad cop dealing with all of them. Biden really might just be the guy for that.
UPDATE: An overcaffeinated member of the so-called Astute Bloggers gives us a right-wing response -- the post is titled "BIDEN!?!?!?!?!? BRING HIM ON! (3 videos)" ... but Biden's really a solid pick if this is the best the "astute" ones have got.