I use acronis true image (purchased and delievered over the internets) to backup the sd card's entire os image to my windows box. After I install a new program, or update my personal menu just as I like it, I copy the new image. That way if anything goes wrong, I have various versions of my tablet in the wings. Flashing a backedup image from my computer to a new card is also very easy with acronis.

Somewhere fanoush gave some instructions on how you can backup your n800's flash without a thirdparty app that costs $. But for the ease and simplicity, the $30 I paid for acronis was well worth it (to me).