lost superblock

[Neal Becker <ndbecker2 gmail com>]

I just updated f11->f12.  After, I followed instructions to convert root 
partition from ext3->ext4.  I used superrescuecd to do it, so filesystem was 
not mounted.

Rebooted into f12 and everything seemed fine.  I also was trying out nouveau 
instead of nvidia, which was OK until I tried to play an hd video.  The 
machine became so unresponsive (seemed to be swapping continuously) that I 
finally had to use the power switch to shut it off (this is a laptop).

On power up, the superblock was corrupted.  I tried fsck, but after trying 
to repair it screwed up beyond all hope, and I had to reinstall.

So, what in the world could have happened?