There is a growing consensus that the best thing for the party to do is to end the primary as soon as possible, freeing Obama to focus his energies on McCain.
I think that would be a waste of the free publicity that comes with the primary, and would give away the natural advantage that the Democratic candidates have right now. As long as the horse race continues, the press will cover it, so why not use the opportunity for both candidates to attack McCain?
The real problem is not the continued race, but the nasty tone and the prospect of damaging Obama, (who is sure to be the nominee). But there's no need for Clinton to drop out; instead both of them could (and should) use the remaining primary season to lay out the strong case against McCain. That double-team would unite the Democrats, protect Obama from friendly fire, and would weaken McCain.