If Tax Penalty For Uninsured Survives, Good Luck Collecting It
Typical clear-eyed view from Jacob Sullum over at reason:

My column tomorrow will consider whether the "shared responsibility payment" demanded from Americans who fail to obtain government-approved medical coverage is properly viewed as a "tax," a "penalty" (which is what the Patient Protection and Affordable Care Act calls it), or both (as Solicitor General Donald Verrilli maintains). That question of nomenclature is relevant in deciding whether the individual insurance mandate is constitutional under the Taxing Clause and whether the Anti-Injunction Act of 1867, which generally bars legal challenges to taxes until they are assessed, makes this case premature. Putting those issues aside, the discussion of the penalty's mechanics by the mandate's defenders leaves the impression that it is unlikely to work as intended even if it survives Supreme Court review.

First of all, the penalty is low compared to the cost of insurance. The minimum payment is $95 in 2014, $325 in 2015, and $695 in 2016 (and thereafter, adjusted for inflation).

...In any case, these penalties can be easily evaded. "Although the act provides that the IRS may not use criminal prosecutions, notices of federal tax liens, or levies on property to collect an unpaid penalty," the Obama administration says in its brief, "the IRS may employ offsets against federal tax refunds. The IRS may also seek payment through correspondence or phone calls." But as a group of tax law professors note in a brief arguing that the Supreme Court should not address the constitutionality of the insurance requirement until it takes effect, taxpayers who know that the IRS has been deprived of its scariest enforcement tools may be less responsive than usual to the agency's letters and calls. The professors also argue that, while the IRS could in theory sue taxpayers for owed penalties, the amount of money involved in any given case is unlikely to justify the effort.

With such low penalties and a guarantee of care, it seems to make sense for people to willfully avoid having health insurance and just pay the penalty. If they're even made to.