My Apple problem

In the summer of 2005, Your Working Boy bought an iMac G5. It's been a good computer in the main, but last summer, the power started cutting out inexplicably. We took it in for repairs. They said it was a problem with the power supply, which they replace for no charge, because it was under warranty.

Earlier this week, the problem returned. The guy at the Apple store said they'd look at the problem, but it would probably be three to five business days before they could fix it ... unless I bought Apple ProCare for $100. I was in a bind: we need the computer to pay bills and manage our household stuff, and we couldn't afford to wait five days. I ponied up. The computer was fixed that afternoon. The Apple store said the problem was with the power supply mechanism, which they replaced. It was a $156 repair, but it was free.

"How come?" I asked the guy.

"You have AppleCare, which extends your warranty for three years," he said.

So this morning I'm sitting here blogging, and pow, the iMac shuts down cold. When I got it restarted, I googled "iMac power supply problems." Lo, it turns out that Apple is aware of a flaw in the very model of iMac we have (I checked the serial number). Apple has a program under which consumers experiencing this problem are able to bring their iMacs in to be repaired free of charge, for up to three years after purchase.

This really chaps my behind (which is easily chapped, but still). I've taken this computer in twice for the same repair, and neither time was I informed that Apple has recognized a design flaw, and promised to repair these computers for free. It seems to me that the Apple store was under an ethical obligation to point that out, and not to credit my having bought an AppleCare policy. Moreover, this fix is obviously not permanent. This week's repair no more fixed it than last summer's did.
We can keep taking it back to the shop for the same repair through summer 2008 -- which is unacceptable, by the way -- but after that, what?

They sold me a flawed product. I want it replaced. It's ridiculous that I have to keep returning to the store for the same repair, and that I'll basically be cut loose after three years. I find it deceptive, too, that they didn't disclose to me that this product is known to have a design flaw. What legal standing do I have as a consumer to insist on a replacement for this lemon Apple? What would you do in this case?