I find the whole discussion about what Hillary Clinton will or will not do tonight to be a little bit hysterical (in both senses of the term).
The facts of the matter are as follows:
* After tonight, there will be no more delegate selection events.
* At some point within the next 48 hours (possibly tonight), Barack Obama will have secured commitments from at least 2,118 delegates required to form a majority of all available. By the end of the week, he will probably have substantially more than the number required.
* Both superdelegates and pledged delegates can switch their commitments. So Obama's nomination will not become final until the convention in August.
* Hillary Clinton will not have a political future if she mounts an active, public campaign to flip delegates.
* However, if some mission-critical event intercedes between now and then, she will of course have an opportunity to argue that conditions have changed and that she deserves to be the nominee. She does not need to be running an active campaign to do so.
* Things like Clinton's tone, rhetoric and behavior could matter in the extent to which Barack Obama is eventually able to consolidate Democratic support. But semantics of a formal "concession" are just one dimension of this, and perhaps not the most important one.
* It is certainly not Clinton's job to announce she is conceding before the final primaries and any sentient press shop would move to quash rumors thereof until the voting is actually concluded.