Actually Jack, don't belittle Bill too much. He especially (Hillary to a lesser extent) really connects with blue-collar voters--and would be a very useful adjunct to Obama's campaign.
She also will be useful in enlisting her own core supporters to support Obama--those who don't already realize the importance of issues like the Supreme Court.

And thanks to Obama's refusal, in large part, to play the gutter-politics Hillary seems to thrive on, it will be relatively easy to enlist the Clintons in Obama's campaign. Added to which, Bill would, no doubt, like to salvage part of his good reputation--and Hillary wants to preserve her options for the future.