Early in his speech at Springfield, he makes clear he won't be shy about throwing punches at his old friend from the Senate:
"Ladies and gentlemen, if your kitchen table is like mine, you sit there at night after you've put the kids to bed and you talk about what you need, you talk about how much you're worried about being able to pay the bills. Well, ladies and gentleman, that's not a worry John McCain will have to worry about... He'll have to figure out which of the seven kitchen tables to sit at."
P.S. As Joe Klein makes clear today, Biden has recently changed his tune on McCain's virtues, saying, "I don't recognize the guy anymore." Such an indictment of McCain from a longtime personal friend could be a powerful line of argument on the stump.
Update: Biden adds in Springfield: "John McCain--and the press knows this--is a genuinely a friend of mine..." and then proceeds to rip McCain for supporting Bush's agenda on the economy, Social Security, and Iraq.