When I think of Joe Biden regarding his capacity for gaffes, I remember one thing.
When he was set to debate Pailin, at the peak of her popularity, which was real and tangible at the time, there was great concern he would blow it. That he'd come across as sexist and condescending, or make a tragic gaffe, or conversely be so accomodating as to allow her to legitimize her presence, winning over voters with unchallenged positions. The result was a display of masterful jujitsu, in which he nailed all his points while displaying perfect finesse, making Palin seem small by comparison without breaking a sweat.
He may not win the nomination, but I think folks underestimate his skill as a politician who possesses what I sense is a genuine, approachable nature.