I've chosen to avoid this topic up to now because the speculation has been so baseless. But for what it's worth, Tom Goldstein, publisher of the well-regarded Scotusblog, is predicting that the high court will not invalidate the insurance mandate. From this morning's post:
There are certainly good reasons to believe the Court will invalidate the mandate. Most important, at the oral argument, the questions of two critical Justices - Justice Kennedy and the Chief Justice - were on the whole critical of the mandate's constitutionality. But in the end, based on the entire mix of information I have, I think the mandate will not be struck down tomorrow. (I don't have any inside information, nor does anyone else.) My prediction includes the possibility that there will not be a single majority opinion for the theory on which the mandate is upheld, and even the thin possibility that the Court will not have a majority to find the mandate constitutional. My level of confidence isn't overwhelming, but it's good enough to give a concrete prediction. We'll see.
TNR's Jonathan Cohn warns that the ruling could take some time to figure out:
When the verdict does come, don't be surprised if the outcome and implications are not instantly clear. The Court could issue multiple opinions, with different justices ruling to uphold or strike down different parts of the law. When the Supreme Court decided Bush v. Gore in 2000, analysts needed several minutes to figure out both what the majority was ruling and what that meant for the presidential election. The same thing could happen this time. More important, this is a complicated case with multiple questions to answer: Is the mandate constitutional? Is the expansion of Medicaid constitutional? If either one is not constitutional, what other parts of the law, if any, may survive? An intriguing, if very thinly sourced, report from Avik Roy in Forbes suggests the justices are still arguing over that last question, which is known as "severability." A solitary sentence in a recent speech from Justice Ruth Bader Ginsburg also hinted at that.
Meanwhile, the Intrade line says there's a 74 percent chance the mandate will go down.