Some Obama purists will be disappointed, but I think they'd ultimately support the ticket. (I don't think they'd stay home or, heaven forbid, vote for McCain.) Meanwhile, you'd get Hillary's supporters, many of whom are yet undecided or plan to vote for McCain, and more women voters. I think it's a win-win.
I just hope the realists in the Obama camp (if there are any, and I hope against hope) prevail. The whole point is to win this election and return the presidency to the Democrats. It's not all about Barack Obama and his high-mindedness and staying above the fray. Get into the fray and let us have a better government. (It appears he's starting to get into it now, but he still needs Hillary to get the votes he needs to clinch the election.)
Idealism is great, but winning is better.