My MBP (13inch, late 2011) sometimes loses it's startup disk when I have powered it off by holding the power button for 10 seconds. Not every time, but one time out of 5.
(See my other question on my MBP locking up when entering clamshell mode for why I have been having to do this.)
When this happens, I get the folder with a question mark. Rebooting with "Alt" despressed, I have to initiate a "network recovery" (only option). In recovery, I select the "startup disk" from the Apple menu on the menubar. All is fine then, but it sure is a pain.
I am using a Crucial M4 SSD, not the stock disk if that matters.
Any pointers would be helpful.
BTW: It might have started with MountainLion. My problem which causes me to need to hold the power button started with ML, so I never reset the mac this way before.