Hillary will never run as Obama's VP. First, she has coveted the presidency for decades. If Obama wins the presidency, he's young enough to do two terms. That's 8 years, and her age will work against her (assuming she doesn't create any new scandals). Second, the Clintons don't embrace former opponents. Bill didn't select any of his opponents as his running mate in 1992, and the guy he did select, Al Gore, by all reports is not on speaking terms with either Hill or Bill. Imagine what terms Hill and Obama would be on after 8 years. Third, why would Obama want to select the one candidate most likely to galvanize the anti-Hillary vote in the general election? Fourth, why would Obama want to have Bill tagging along after the problems Bill has caused? Fifth, the people who want to see Hillary as the first woman president won't be as enthusiastic about her being the first woman vice-president, so Hill will not bring as many voters with her as she's doing now.
As for Obama being Hillary's running mate, again, the Clintons don't embrace former opponents. Second, Hillary doesn't particularly want to share the limelight with Obama's star power. Third, it would send a signal that Hillary can't get elected on her own; she needs a man to do that. Fourth, the people who want to see Obama as the first black president won't be as enthusiastic about him being the first black vice-president, so Obama will not bring as many voters with him as he's doing now. Fifth, Obama is young enough to try again for the top prize and has no need to link himself to the likely scandal-plagued and ineffective Hillary presidency, if she wins the election.
It just ain't gonna happen.