Republicans are saying what you'd expect them to: we won't engage in sham negotiations. If you want us to come to the table, shelve this monstrous and unpopular plan and let's start over.
Democrats should recognize the tactic: they invented it. And used it successfully against Social Security reform in 2005. Sure, they wanted to do Social Security reform, they said. All Republicans had to do to bring them to the table was get rid of the central point of the reform: the private accounts. Astonishingly enough, they did not suffer at the polls, even though the president tried to stir up public discontent with their "obstructionism". The problem is, the public doesn't get mad at you for obstructing things the public doesn't like.
The GOP Congressional delegation would be idiots to agree to serve as human stage props for a White House-controlled event that inevitably will be rigged against them. Especially because Obama is still more charismatic, smarter, and a better debater than just about anybody on the GOP side. Wrong but sharp.
Update: I think Andrew Sullivan's got a valid point that "not showing up makes [the GOP] look totally obstructionist and makes Obama look more responsible and presidential." Maybe the political optics require the GOP to show up.
On the merits, however, it still seems clear to me that the summit is intended by the White House as a political trap. It won't be a meaningful negotiation, since the President is coming in with strong preconditions, as the White House's latest statement on the summit makes clear that:
The President is adamant that we seize this historic moment to pass meaningful health insurance reform legislation. ... What he will not do, however, is walk away from reform and the millions of American families and small business counting on it.
<Tongue in cheek> I'm tempted to insert a crack here about how the President is willing to negotiate with Ira and North Korea without preconditions, but that would be the sort of cheap debater's ploy with which the summit will be rife, so I'll pass. </Tongue in cheeck>
Unless the President is willing to terms and conditions that make the summit a level playing field in which both sides ideas will get fair representation and a fair opportunity for inclusion in the bill, the GOP should skip it.
BTW, McArdle also catches the NYT in a bit of an inconsistency when it comes to "obstruction." Amusing.