My NSLU2's root partition ("/") got corrupted due to a power failure. Symptoms were:
I tried first to run "shutdown -Fr now", but that did not help. This command is supposed to invoke fsck upon reboot.
The way I fixed the issue was to shut down the NSLU2 (using "shutdown -h now"), disconnecting the disk and connecting it to a Windows XP computer running a VMware? image of Debian Linux, running "fsck -fcyv /dev/sdb2" (where /dev/sdb2 was the device address for the new disk - you must umount the disk if it gets mounted automatically before you can run fsck). It took almost 30 minutes but the recovery completed and, upon reconnecting the disk to the NSLU2 and pressing the power button, I had a functioning NSLU2 within minutes.
Writing this here for my future reference as well as others. Please refer to manpage for fsck for each of the flags and use these instructions at your own risk.