I have recently been playing with various ROMs and returning to my Cacko 1.21b install which is excellent in the functionality and I'm loath to change it at present.
I was using NAND Backup/Restore and I noticed that I was getting jffs2 errors about some inodes associated with files that no longer existed - the messages then said unable to remove the inodes, these errors persisted over as many reboots as I had care to try - this was immediately after a NAND restore so there were two possibilities, either I had some duff NAND flash or I had captured a corrupt NAND image. I ran a full NAND check and it reported 0 errors so in the end I ended up restoring the NAND flash, taking a backup of it, untarring the backup and diffing all the package and library files just to be certain that they were intact (phew they were!), using the 3rd option on the Japanese startup menu (Hold down OK on battery insert boot) to erase the user partition and finally restoring the backup. This got me back to a clean state with no duff inodes which the kernel couldn't delete (as was the case with what I had before).
My observations on this are that such corruption shouldn't really happen but if you are playing and you do manage to crash the Z stone dead then it's possible. What you should then do is really examine dmesg output and if you see jffs2 errors probably shutdown and restart again to see if the kernel checks managed to clean it up.
Now the only recourse that I had to clean up and retrieve my data was to format the user partition and tar everything back, however, this is going to be a problem with pdaXrom which had a writeable root and also with OZ because it has writeable root and for some reason seems NOT to erase the home partition with the aforesaid menu.
I would be VERY interested if anyone has any suggestions on how to fsck these mtd partitions and to force deletion of orphaned inodes that a standard check can't get rid of, maybe this could be achieved by booting off an SD or CF card with the jffs2 partitions unmounted but there doesn't seem to be an fsck.jffs2 knocking around.
Any good ideas ?, this would probably be useful, as I mentioned, for pdaXrom and OE guys too.