I always unmount the "drives" before I unplug, there is definately nothing wrong with the usb port as I use it for my n800 and other usb drives and haven't had a problem before.
No way of knowing if it is the cable, but I doubt it as it see's the drives ok, then everything goes badly wrong after I use it.
Given my current experience with the N800 and N810 I'd say there is something badly wrong with the memory card handling somewhere.
I've had some weirdness on my n800 since upgrading to OS2008 related to memory cards, (had to take battery out for 5mins) all stable now, but I'm leaving them well alone for the moment until my USB sd-card reader arrives then I can shutdown my N810/N800 take the card out transfer data to/from it and then put it back in - just way too unreliable and I don't want to lose data again.

Unless there is a formatting difference between the N810 and N800 and it's the swapping them around that stuffs them?

mmmm....I'll try reformating my external and see if that helps
(it seems to have helped, maybe that is all it is?)

Is there anyway of "securing" the memory card in as it may be slipping out?

Cheers,

Malc