In the end. I'll cut to the chase. My 27" 2010 iMac has been laced with faults from the beginning but I've also had some use out of it over the past two years. Recently, the same fault with the GPU reappeared and I went as far as Executive Relations to try and get it swapped out as I thought the machine was a lemon. Unusually, Executive Relations were useless and completely refused to help me other than repair it again. I didn't accept this, and instead emailed the store manager at the Apple store I purchased from. He asked if he could take a look at it and I agreed. So, yesterday morning, only an hour or so after speaking to him, he had a specialist courier collect the iMac from me to save me lugging it into store. After a couple of hours, I got an email from him stating they'd replaced several parts and were running extended tests on it overnight. First thing this morning, I get another email telling me that their extended tests have revealed it is broken beyond repair and they are just going to replace it for me. This was at 11am. I was offered the 27" 2011 model and upgraded to the top of the line version (3.1GHz). In addition, I have been given a brand new, full 3 year warranty on this new machine. This alone was an excellent gesture. However, less than 1 hour after the manager doing the exchange and receiving the new receipt for my new imac via email - a courier arrives at my door with the iMac. The store is about 40 minutes away by car. Stunning service. Just stunning. All in all, it was less than 24 hours and I didn't even have to leave the house.