We experienced an issue yesterday trying to update the iMac my wife is selling to her friend...it stopped mid installation and said that the install couldn't complete because the hard drive was damaged and needed to be repaired. This hard drive has had no issues before, and looking at it in target disk mode, still had no issues with it...but for some reason Mavericks would not write to it properly. After making sure we had a back up, we attempted it again, and got the same message. We scheduled a genius bar appointment for tomorrow because it's still under warranty, and if the hard drive itself IS a problem, I want them to replace it.