Too much is being made of John Roberts' decision. He didn't rule in Obama's favor because he AGREES with the ACA. He's not ENDORSING obama's plan, he just doesn't think there's a question of constitutionality.
It's a crafty opinion in the best traditions of the SCOTUS, really. The Commerce Clause doesn't allow the government to regulate inactivity...but it's still legal because it's a tax and the government can tax anything it wants to...as long as the taxes are not "obviously designed to regulate behavior" outside federal jurisdiction...and despite it being a tax, the AIA doesn't apply because it's not CALLED a tax, which matters for issues of statute but not for constitutional ones. In other words, it makes the "correct" ruling (since everybody agrees that you could change half a dozen words in the law and it would be constitutional and do the exact same thing, so it's not like Congress just doesn't have the power to do it, they just had a typo) but does so by limiting federal authority, calling on a different and stronger Constitutional power, and asserting that case-by-case judgement is necessary to apply the precedent. Marshall would be proud.
edit:
But the IRS can put you in prison. And forced prison sex is very real.
The IRS explicitly can't prosecute you or put a lien on your assets for not paying the mandate penalty -- it's in the ACA. They can presumably make your life difficult in other ways. If you were expecting a refund, for example, they can garnish as much of that as they want.
