Just some more information - this thing is really behaving in a crazy way. Computers are supposed to be consistent, you should be able to get repeatable results when you do the same thing over and over. But this one is most definitely not behaving consistently.
I've been attempting to boot from the UniBeast (1.7.0 for Mountain Lion) installer. It always fails in some manner, but it's different every time. As an experiment, I've booted it repeatedly without making ANY changes to kernel flags or anything else (always doing the same thing). I get very differing results each time.
Sometimes (rarely) the installer will start up, but then crash before I can begin installing. It crashes in two ways - either the installer log window pops up, with a few error messages in it (I haven't yet been able to capture the log because it usually KPs while I'm trying to save it). But the errors are varied - All of them are from a program called "LCA" (I can't fathom what that stands for). One says "NSSoftLinking - The Librarian framework's library couldn't be loaded from (null)". Another says "The function 'LBCurrentProcessHasUbiquityContainer' can't be found in the Librarian framework." Then there's usually a message about bootp failing and a message that "DHCP en0: INIT transmit failed".
Sometimes when I boot from the UniBeast USB, I get the gray Apple screen with the spinning circle, which stays up forever (along with the LED on the USB key blinking). Don't know what that's about!
Often I just get the gray "mesh" background and nothing else shows up. Other times I get a KP (the dark gray box that says "You need to restart your computer" in a zillion different languages). This inconsistency doesn't make any sense, unless there's something really wrong with my hardware (but even that, it seems, would cause more consistent failures).
This is my fourth Hackintosh build; I've never run into this kind of problem with any of the other three. I'm at my wit's end here. Does anyone have any clue what's going on?
UPDATE: I am able to get consistent, predictable behavior in one instance: When I boot from the UniBeast USB drive and enter the kernel flag "GraphicsEnabler=no", I always get a kernel panic that looks like the screen attached. Can someone more knowledgeable than I take a look at this KP and tell me if there's anything useful to be learned from it?