Using an "Et tu" argument means you arent actually addressing the original criticism, you're saying "You do what you accuse me of and therefore you have no right to accuse." But it doesn't actually address those accusations as one can be a hypocrite and still be right in his accusations.
Also what youre accusing Biden of in your posts isn't the same thing I was accusing O'Donnell of, so its not even an "et tu" argument its just "well you aren't perfect either" argument.
Well I got two things to say:
1) I'm not Joe Biden
2) That doesn't address the point.