In the 7/23/2012 American Spectator, David Catron describes how "The IRS Illegally Expands Obamacare Tax Credits".
As Catron notes, the feds will attempt an end-run around the law by distributing certain monies through federal "exchanges" even if the law as written only allows the states to do so. This would nullify the attempts of various anti-ObamaCare governors to block the law at the state level by declining to establish state-run exchanges.
But even if the legal problems are clear-cut, we now know the courts will not likely uphold legal challenges to such actions. Instead, they'll likely defer to what they regard as the will of the legislature.
US Supreme Court Chief Justice made that very clear when he wrote: "It is not our job to protect the people from the consequences of their political choices."
Which means it really comes down to the voters in November.
Update: Catron notes that two Congressmen have introduced a bill to try to stop this maneuver.