Alright, after filing down the edges of my mini-A cable, it now fits the mini-b port in my n800.

Working / Working-ish:
Sandisk Cruzer Micro USB drive (mounts and filesystem works)
Apple USB keyboard - Typing possible, capslock doesn't light up but still works, errors about "USB hub not supported". Hub does in fact work - I can plug the Cruzer Micro into it.
BU-353 GPS - After insmodding pl2303 drivers, works fine with gpsd and maemo-mapper.
Nikon D40 - works, mounts card.

No driver yet, but appears to work:
USB Prism2 wireless card - Recognised - will have to compile driver and see what happens

No driver yet, not sure if it will work:
Keyspan USA-19 USB PDA Adaptor (usb to serial): Caused device reboot, shortly after unplugging. "USB hub not supported"

Not working:
Legend card reader - lights up, can't mount the SD for some reason. Might be because there are multiple units available...