I torn about it honestly. The fact that the insurance companies are fighting it makes me think it'll be good. But from what I hear I'm not sure how it'll be enforceable. (You exist, thus must have health insurance, oh? can't afford it? uhhh... hmmm...) Also, I don't generally consider myself a constitutionalist, so this doesn't bother me that much, but I am a little confused at how it was ruled constitutional.
But really, I also don't quite understand why the insurance companies are fighting it. Wouldn't this drastically increase their profits? Or am I missing something?
I'll take a crack at answering your questions:
The enforcement of the law comes through the IRS. When you do your taxes each year they're be a box on the form asking if you have health insurance, depending on the answer your tax return will be more or less. The penalty currently being $695 or 2.5% of your families income, whichever is higher.
The constitutionality comes into play because they made the case that Congress has the ability authorize new taxes, and that the mandate fell under that authority.
Finally, the reason that insurance companies are fighting this so much is that there is a new regulation that requires them to use 80% of the money coming in for health care costs. So they won't be seeing the mega profits that they had in the past. Hope that answers your questions.