At first blush this may seem a delicious irony:
The penalty applies to any period the individual does not maintain minimum essential coverage and is determined monthly. The penalty is assessed through the Code and accounted for as an additional amount of Federal tax owed. However, it is not subject to the enforcement provisions of subtitle F of the Code. The use of liens and seizures otherwise authorized for collection of taxes does not apply to the collection of this penalty. Non-compliance with the personal responsibility requirement to have health coverage is not subject to criminal or civil penalties under the Code and interest does not accrue for failure to pay such assessments in a timely manner.
http://www.jct.gov/publications.html?func=startdown&id=3673This means: no enforceable penalty means people have no need buy insurance, which means they won't pay into the pool. But insurance companies can't deny coverage for pre-existing conditions. That means you can sit out paying premiums and only buy insurance when you get sick.
This will bankrupt the insurance companies in record time.
Once they go bankrupt you better believe single-payer is mere minutes away.