Mywork MacBook Pro wouldn’t boot up.  It was hung on the gray screen with the apple logo and the spinner spinning.  THIS article told me what to try and fortunately, the save-boot did the trick.  However the safeboot booted into the blue screen and I had a mouse cursor I could move but Finder did not appear.  I turned it off and back on and it came up all the way. This article has more details on the problem.

Update: Next day wouldn’t boot up at all. Was stuck on blue screen.  I took the following steps to backup files:

• Reboot and hold down <Command> S to boot into Single User Mode shell
• /sbin/fsck -fy
• mount -uw /  ; Make drive writeable
• mkdir /Volumes/usb
• ls /dev/disk*   ; Locate usb drive, should be last one listed
• /sbin/mount_msdos /dev/disk2s1 /Volumes/usb
• cp -r srcFolderName /Volumes/usb
• /sbin/umount /dev/disk2s1  ; !!! Important. Unmount before removing drive