I am experiencing this problem as well... plugging in a USB keyboard to my N800 disables the onscreen keyboard (good)... both unplugging the keyboard or unmounting the USB keyboard by clicking on the icon on the top bar *then* unplugging the keyboard fails to bring back the onscreen keyboard (bad).

The only way I know how to re-enable the onscreen keyboard functionality is to reboot the unit. Anybody come up with a solution that doesn't involve a reboot? Thanks for any help...