The legal challenges, at least so far, seem to be focused on the mandatory coverage provisions that don't go into effect until 2014. I doubt if any court would accept a suit to delay the entire program in order to address that part (dumber things have happened, of course).

These challenges focus on the idea that a Federal law imposing an obligation on the states is precluded by the 10th Amendment. The Supreme Court addressed this, on the topic of Social Security and Medicare, in 1937, and found that a national law that addresses the general welfare of the citizens of the entire nation is constitutional. (Look up Helvering v Davis, if you'd like.) It would be very interesting if the current Court found the health care program unconstitutional - then where would Social Security be? Besides broke, that is.