You need to fix the poll options. There are many people who have only had less than 3 iMacs and were obviously not happy. So if you had only one iMac, but decided to keep it despite if it was defective, what do you vote?
What about those people that are on their 3rd, but gave up afterwards (hence, not a charm)?
And then there's the people who got a nice one on their 4th. And others still stuck with a defect after their 5th.
I wrote a theory about why exchanging iMacs in Apple Stores is very different than exchanging through an online order. I think the real random draw comes from the online delivery, where as if you exchange at the same store, you would likely be getting another draw from the same bad batch. (It won't matter if you are on your 7th replacement if all of the iMacs in that batch carried a defective display or HD).