OK I have now reinstalled my SD card in the 450G. I managed to slide two layers of paper underneath the SD card in the slot. I also pulled back the card about 1mm from the end of the slot.
So far so good, 12 hours and the disk is still present.
I moved the user-manager and web-proxy stores to the SD card and my "blocks written per hour on the NAND" stat went from a whopping 10,000+ to less than 1,000.
So if my calcs in this post
are correct, the NAND should now last 100 years...