I'm running Ubuntu 10.10 x32 and I couldn't use my Pendrive in my virtual operating system.
For those having the same problem as I had with usb devices:
1º Download and install Virtualbox from www.virtualbox.org
2º Download and install extension pack from the same site.
3º Once installed open the Virtualbox
When I tried to go to the option USB a window appeared saying: "Failed to access the usb sybsystem" If not, you can stop reading.
4º Go to the Accessories > Terminal and introduce:
if [ "`grep vboxusers /etc/group|grep $USER`" == "" ] ; then sudo usermod -G vboxusers -a $USER ; fi
Press enter and introduce your login password. After that it seems that nothing happened.
5º Reboot your computer.
6º Connect your Pendrive.
7º Open Virtualbox and go to USB. Hopefully you won't see the message again.
8º Choose "Add filter from device" (its icon is a usb wire with the symbol + " And now the name of your Pendrive should appear. Select it and press OK
9º Run your guest operating system who should now detect the Pendrive.
10º I hope this was of some help.