I encountered problems to connect my n810 to a PC via USB. While the external memory card is connected successfully, the internal card cannot be accessed via the PC (running a Ubuntu system). When I try to unmount the card the following statement is displayed:
umount: cannot umount /media/mmc2: Device or resource busy
Searching the forums I found only a reference in the German n800.de forum. Yet, the proposed workaround (to connect directly w/o intermediate usb-hub) does not work for me. Up until now, the only solution I have found is to reboot the system. Which is feasible yet not very convinient.

Maybe somebody knows a way how to calm down the memory card - preferable w/o killing all processes by hand?

icke