But I finally got the mistery solved: the Group ID from VBOX wasn't in
the USBFS-Entry. More detail here:

http://forums.virtualbox.org/viewtopic.php?t=10661

What a difference from VB for Mac OS X! It was just ready to use with
all its funcionality (USB included) right after the install was done.

Sometimes I wonder why things on Linux need to be such a pain...