My 2012 Air was a lemon. From the outset its wifi kept dropping and needing to be rebooted. Then the power charging became intermittent. Then over the summer the hard drive died. I had the 3 year warranty so even though it was 14 months old Apple replaced the SSD. A few weeks later I returned it to deal with the wifi and power issues. They took it overnight and replaced the board for the charger and the lid/screen. They also flagged up a battery issue and replaced that. But on getting it home the wifi issue was still happening. I reinstalled OSX to no avail. Happily they are now exchanging it for a brand new 2013 model. But the question the 'genius' couldn't answer was what happens to the warranty. At the moment I have 20 months more Applecare. Does it carry over to the new machine? Is it 'reset' to another three years? Just wondered if anybody has experience of this scenario.