That worked a treat! In case it's helpful for anyone else, it looks like the point I screwed up at was thinking that the "skip this" warning on step 4 was more-or-less optional. Also, the only point I deviated from bodhi's instructions above was in editing the fstab to reflect the fact that I couldn't seem to get Ubuntu to let me format the card I used in ext3, soby the_wondersmith - uBoot
I PM'd bodhi for advice about restoring the MTDs on my PogoPlug v4. He requested that I make a new thread here, I'd imagine in the interest of helping anyone else that's gotten themselves in the same situation I have. To recap -- I (naturally) messed up my PogoPlug by not reading carefully enough when flashing and by also not keeping a better record or any kind of backup ofby the_wondersmith - uBoot