People will pay the yearly fine until they have a major health problem, and then join up after the fact. There are some limitations on this, though not airtigh

People will pay the yearly fine until they have a major health problem, and then join up after the fact. There are some limitations on this, though not airtight ones. If you don't enroll in the initial open-enrollment period from October 1, 2013 — March 31, 2014, you can't enroll completely freely after that. Subsequent enrollments are allowed only when you have a "qualifying life event", such as a change in employment situation, or a move between states. The main one that's clearly health-linked is that you can enroll upon pregnancy or childbirth (the argument for that appears to be based on the desirability of the child having health coverage, even if the father and mother were previously remiss on the subject). But it doesn't appear to be the case that you could just wait until you have a motorcycle accident, and then enroll for treatment.