Thanks for relating that horror story, good to be warned. Here's mine, from last night:
I have an AMD64 system with Debian and Ubuntu (and MS Windows Vista), each on a single partition (but different hard drives). The "working" GRUB is the one from the Debian system. After I booted into Ubuntu and did some updates I rebooted into Debian. Horror: fsck failed on root fs, cannot find superblock, read-only mode. I too could not find the superblock. Bah!
Eventually I rebooted into Ubuntu, and was told that drives are being checked. So I notice that fsck is working on the Debian partition (which I mount in Ubuntu to make accessible easily). After fsck completed there, apparently problem-free, I could boot happily into Debian.
I conclude that perhaps I had shut down Ubuntu while it was doing an fsck on my Debian partition, and this interfered with Debian's own bootup checks and fsck. Odd indeed, linuxes interfereing with one another. Gave me a right fright, that did.
