all looks fine (flasher should be run as root too?), without seeing output it is hard to say it for 100%

So then you did 'umount /media/disk', moved card to the tablet and booted it without installing bootmenu or otherwise messing with initfs partition at all? And root filesystem is mounted read only? What firmware (kernel,initfs) is flashed on the tablet, same Diablo?

Yes, flasher was either sudo or su as well. there is no output errors, maybe there's a verbose report.
I tried to do a chmod but it wouldn't let me touch anything.

I think it's the partition somehow. I tried to copy it all over again, and I copied to media/disk instead of media/disk1 as I (apparently) did the first time.

However, media/disk would not let me write anything to it, no permissions. The other ext2 partition had no complaints however.

Unmounting and deleting the partition allowed me to move the existing one, going to try and mount that one... moving it apparently erased it instead of moving.
Great.

So.... one more time.

Finally!! Everything works on when I boot from SD. I even went and installed a bunch of my favourite programs again. :-)
It must have been related to the ownership or something, I had to go in as root and chmod everything to 0777... EXCEPT /etc/sudoers which has to be 0440.

Now to figure out how to backup (and restore) it... Actually, a couple more things as well.

How?! Can't figure out what device or whatever it is. My Linux use is limited to mostly user so far.

Can we use that memory for swap/virtual space?

Also, to make a backup of this, can I just do a copy to another card? (Ok, maybe another tar at least)

Finally, is this worth putting together into another post or wiki article "How to create a bootable card on your PC - booting tablet not required"

mount -t jffs2 /dev/mtdblock4 /opt

Well, you can do anything but this is not a good idea, jffs2 compresses data by default when writing which is slow. Also it is not a filesystem suited for a lot of writing. IMO the best usage for it is to keep clean bootable system there for recovery when your main system on mmc breaks.

yes

Yes! THANK YOU so much for all your help, Fanoush!!

By the way, your ITT message box is full, Fanoush... no doubt by all our newbie pleas for help

Total awesomeness! At last I can backup my comic bookmarks! ;-) I mean, save my valuable phone numbers, addresses and other data.

Ah, yes. I was thinking of reformatting the flash to swap but a working, recovery spot is probably the best idea, given my usual "test to destruction" behaviour.

Perfect! Eh.... except my external card seems to have mysteriously vanished. I hope it didn't pop out somehow when my N800 fell out of my pocket while I was running to the car through the pouring rain on the weekend. Everything else that detaches came off except the (secured) internal card. Dried it off before daring to put the battery in again; thankfully it didn't fall into an actual puddle.
[edit] for all those of me worrying, found it whew!

Anyway, thanks again. I hope other people can use this too. I'll put everything together in one final post to this asap.