I have another question that may have been addressed. What happens to the people who still refuse to purchase insurance? Do they get a bill in the mail? Or does the penalty come from the $10,000 tax refund check they didn't earn?
My understanding is that the I.R.S. will be in charge of enforcing this. Not because the Court ruled it to be a tax. I'm relatively certain they intended for the I.R.S. to enforce it all along.
Assuming that it is the I.R.S. that enforces this, they will have some sort of reporting requirement. In all likelihood, companies which provide health insurance will be required to submit a form for each customer verifying that they are covered by insurance.
If someone over the age of 18 files a return, and the I.R.S. system notices that no health insurance report was filed on their social security number, then they will mail an inquiry. If no response is received, then they will send an assessment of the amount owed. If no response is received, then they will send it to collections, who will levy your bank account and garnish your wages.
While in collections, they'll keep any federal refunds you are due and apply it to the balance you owe. They'll also file to intercept your state refund.
I assume businesses who fail to properly report an individual who does have insurance through them will be fined with a civil penalty. Those businesses who currently fail to properly report and/or file employment withholding often get hit with civil penalties. The same collection technique is used: send notices, wait for response, move to collections, take money.
They are a pretty cost efficient agency.