MBA 2010, upgrading from Mountain Lion. 256 gb SSD with 90gb free. As it was installing, a dialog box pops up on the screen and said something about the disk being corrupted. It gave me some disk utilities so I ran a verify disk. It identified a corruption and asked me to repair disk. But the "repair disk" option was greyed out and unselectable. So I rebooted into Recovery Mode per a poster's recommendation at Apple discussions and tried to repair disk from there. No go. Error message says it cannot be repaired and that I need to backup the disk. We'll I don't have an external hard drive or time capsule - just a 16 gb USB drive. I rebooted and tried the installation again. It seems to be going but I still have 15 min left. Hopefully it works, but just wanted post this in case someone else has this same issue. A lot of people over in an apple discussion group had the same problem. Have to admit i'm disappointed that such a huge install bug slipped passed Apple's QC.