Had mine replaced last week for free. It's the second time it has gone, both times the cards lasted for exactly 2 years and 9 months before failing. Apple initially said no to me in store and were going to charge £500+ until I gave a consumer law argument that the product was sold by apple defective, and then replaced with the same defective part (hence it has failed again). That argument worked for me in the UK, but expires after 6 years so it won't work again! It also only applies where the product was bought from apple direct, as consumer law responsibility applies to point of sale. I know I've been lucky but it is still not nice to know I have 2 years and 9 months to go now before my iMac (which is otherwise perfect) dies again, and presumably at that point it will be declared vintage and parts unavailable.