Another way to get data off is to flash fanoush's initfs and use telnet to mount rootfs and ssh to download files or even that /dev method of retrieving the code. This would require another tablet to generate a image however and linux knowledge to flash an initfs image on computer.

"# Having trusted pairing with any BT device (whose MAC add. he might be able to get while/before he gets your N800)"

I don't see this as a risk. It would mean having bluetooth enabled before locking and osso-systemmui-early which handles startup locking, has no bluetooth services running before it afaic.
Do bt file browsers work against the n800?
I guess if you leave bt on while locking the device while on, this could be a risk.
"# Autoconnecting to WAPs and running ssh-server with easily guessable password"

My n800 connects after desktop is loaded

But once again, this could work from a lock after booting while the n800 is still on.