Funny Hillary should come up.   She has at least as much right to be considered as Democratic nominee for 2012 as Biden does--perhaps more---and her supporters will not be shy about saying so. Her supporters will also not be satisfied with giving her the VP slot under Biden.
And Biden, once made president, will not likely accept the #2 spot under Hillary.

This is the most likely reason for bloody primaries on the Democratic side if Mudcatters' idea about Obama stepping down now is adopted.

It is, bluntly, one of the worst ideas imaginable for the Democrats.