In the speculation about whether or not Senator Obama will pick Senator Clinton as Vice President, the question I’ve not seen anyone ask is whether she should accept if asked. I think she’d be wise to refuse.
If Obama wins, she will get no credit for it- even in a normal year, it is conventional wisdom that people vote for the top of the ticket, not the bottom; and this time, with the Republican party at its nadir and Obama being so charismatic, she’d be seen as unnecessary icing on the cake. Should Obama lose, rightly or wrongly she'd be blamed for the loss, as Ferraro was before. There is simply no upside for her in the campaign.
Should they win, Obama could not afford to give her any real power. If she had power and success, the Cheney to his Bush, then with or without her permission her followers would paint her as the power behind a charismatic figurehead- it would be the perfect setup for her own run eight years from now. Obama could not allow that, and not just for his own ego; it would be the ultimate irony if the first black President was seen as a token figurehead. There's no way he'd accept that legacy. On the other hand, should she be given power and fail, President Obama would get the blame in the end, and rightly so; "the buck stops here." Therefore, should would never be given any real power in an Obama administration.
If she were to serve as Vice President without any specials powers, she'd suffer the fate of all such vice Presidents: instant obscurity. That would give Nancy Pelosi another eight years as the most powerful woman in America, making her a serious threat to Senator Clinton's chances to become the first female President. On the other hand, should Hilary stay in the senate, then given Senator Kennedy's poor health and the fact that Senator Byrd can't last forever, she will quickly become the public face of the Senate, a perfect place to launch her next campaign from. the one and only thing she gains from serving as Vice President is the chance to become President without standing for election should the unthinkable happen, and the last two Presidents who reached the office that way, LBJ and Ford, were not successful.