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Basically, if you have a mid-2011 Core i7 27" iMac with the Radeon HD 6970M video card and the video fails, Apple will replace it for free for three years after purchase. if you've already had the video card replaced and were charged for it, you can request a refund. I've got one of these and I seem to remember a couple of other forumites bought them too. So far, no issues (and to be honest, my opinion is if it's not had a problem so far it probably isn't going to).

My serial number is an affected model but I haven't had an issue with the video card yet.