I have a late 2009 MBP and was running ML and tried installing Mavericks GM twice with the same error occurring. The second attempt I followed the directions that used the terminal to build a bootable install usb and after the install my computer would reboot and display the grey screen with the apple logo and the spinning grey loading thing. After a while the spinning grey thing disappears and the computer seems to be stuck on the grey screen with just the apple logo. I can use my mouse but the computer never seems to get past this point. Has anyone else gotten this issue? I am also wondering if my bootcamp partition affects the install? I am currently using my bootcamp until I can get home and restore my ML.