Although i have set everything correctly (the usbcam file, it is owned by root:plugdev and i s executable; usermap file and everything else) my camera is not accesable by a user that is not root. My user is in the groups usb, plugdev. Tried everything but nothing helped until i found http://forums.gentoo.org/viewtopic-p-3386425.html#3386425 This solution helped. So i think there is a problem in the current sys-fs/udev-096-r1 is somehow wrong. Maybe the ebuild of udev could add a generic rule that sets correct permissions for all devices/cameras.
*** This bug has been marked as a duplicate of 125788 ***
