I have found the built in backup app to be only marginally useful. It does help after flashing the device but I still have manually install things that did not come from reposities and the settings for only some apps get backed up.

Below is what I do "normally" when not going between device updates.

I setup to boot from the removable memory.

I have 3 of the same memory card. I use the cp command in linux with root privilages to copy the contents of one card to another.

I generally have two partitions on the card. A 500 meg ext2 partition that I boot from and fat32 for the other partition.

Each time I want to backup I shut down the tablet mount my oldest card on my linux machine and format the two partitions. I then mount my newest card that I just pulled out of the tablet. I then copy the contents of the newest card to the freshly formated oldest one.

The old card (with the new copy on it) then goes into the tablet for use with the next most recent card carried as a spare (my case has couple of pockets I use for this. The oldest memory card stays at home for safe keeping.

I have had the card in use get corrupted on it's own, or with my help a , a few times this has worked out well.

My frequency of doing this depends on how much stuff has changed on the table and how painful it would be to redo it if things went bad.