Here is a top-ten list of his gaffes, from Time Magazine. I particularly liked when he said, “I’m told Chuck Graham, state senator, is here. Stand up Chuck, let 'em see you. Oh, God love you. What am I talking about. I’ll tell you what, you’re making everybody else stand up, though, pal.” It was a gaffe because he had forgotten (or didn’t know) that Chuck Graham (state senator from Missouri) is wheelchair-bound, due to paraplegia.
He’s not notably gaffe-prone if your metric is gaffes per million words. 
The man’s simply in love with the sound of his own voice. It gets him into trouble sometimes.
My favorite one is not on that list:
[QUOTE=Joe Biden]
Now is the time to heed the timeless advice from Teddy Roosevelt: ‘Speak softly and carry a big stick.’ End of quote. I promise you, the President has a big stick. I promise you.
[/QUOTE]
Gaffe (n.)
When a politician is caught saying the truth out loud.
Obamas biographer Ed Klein noted that the campaign asked Clinton weeks before the functionally retarded Biden made racially divisive comments in Virginia followed by 2 other predictable gaffes.
It is true that the weekly standard has a partisan agenda but it really no different than msnbc or newsweek choosing to ignore Ed kleins claim because it does simply portray a campaign in trouble. Just because everybody ignores it does not make it irrelevant.
Example… David Plouffe taking money from suspect orgs in Nigeria then donating to democratic orgs once a little light was shined on it. It IS unethical but will not matter because of media blackout
Biden will not be replaced for 2 resasons
a. Clinton does not want to be tarnished by Obama not being re elected or by the fact that the democratic party will be even less popular in 2016 after 4 more years of Obama
b. Obviously it would show desperation. Yes FDR did it 3 times but this is not a practice of modern electoral politics and the all media would view dropping Biden as exactly what is would be- Desperate.
“Shades of Vince Foster?!” -Matt Drudge