If you find in Google any Ubuntu solutions, these do not work for Fedora!
http://forums.fedoraforum.org/archive/index.php/t-162084.html
1. Create a new group called “usb”
2. Locate file usbfs: in my case is /sys/bus/usb/drivers (I suggest to find the file with a usb device inserted)
3. Modify file /etc/fstab inserting a line containing the right path and the number corresponding the “usb” group :
none /sys/bus/usb/drivers usbfs devgid=503,devmode=664 0 0
4. Issude a command
mount -a
5. Start VirtualBox