This is basically me just bitching at this point but I think something is wrong with the Momentus XT in my unit. Every so often I'll get a hang in the system (typically close to booting up) and then I get that error msg followed by the drive dissappearing (D in this case, the Intel 510 is my main drive). It has "come back" every time it's gone away after a reboot but I've now seen it between 3-5 times.
Also, something is making a squeaking noise. Argh. Something tells me I'll be popping this thing open again to remove the drive and start the troubleshooting there.
... I really hope it's not the Intel SSD.