The New York Times has pretty much declared the battle for the nomination over. It analyzes the numbers and concludes that, barring some shocking turn of events, Obama will be nominated.
So why not just pull the plug on this thing after the next round of primaries. After all, if Clinton is going to turn this around, she has to do it in Pennsylvania, Oregon, North Carolina etc. If by some miracle, she actually pulls ahead in elected delegates and the popular vote, keep the battle going. If not (and the Times' makes clear that ain't going to happen) the super delegates should simply declare their choice and the nomination can be decided.
Rosenberg makes some points that I definitely dispute, such as the argument that a long nomination will hand the election to McCain. I think the primary advantage of Clinton staying in for the time being is that McCain is getting very little coverage. But for that Democratic lime-light strategy to work, Clinton is going to need to change tactics in the next few weeks - and already shows some signs of doing so. She seems to realize that the kitchen-sink approach was a big mistake, and hopefully she won't reprise that for Pennsylvania. She needs to start giving some subtle props to Obama, such as she did regarding his speech. In other words, she should stay in for now but subtly change her campaign from a Clinton campaign to a Democratic campaign.
The thing is, it's difficult to tell whether her campaign folks really understand that it's over. Judging from Mark Penn's quotes in the NYT article, they think that they're in a perfect position to clinch the nomination. And that's a scary type of delusion.