It massively corrupted my filesystem last night, but I think this was my fault, with what was in hindsight a horribly buggy tuxonice-debugging patch, which broke proper suspension of the block devices, following which ext4 tried to write to them, stamped on its own superblock then panicked and rebooted, leaving me with a desynchronized RAID array and all mounted filesystems with badly mashed block group descriptors and superblocks.
But fsck fixed them all flawlessly (zero differences from backup, I owe tytso yet another beer, by this point I owe him so many he could kill himself with alcohol on my tab) and I blame my own broken patch anyway.