The current samba-3.0.20 ebuild does install a man page for umount.cifs, but not umount.cifs itself. I think this is import, because (u)mount.cifs is the only solution to mount a CIFS share as user instead of adding the share to fstab. Please include umount.cifs (which is available since 3.0.20). Thanks.
*** Bug 104505 has been marked as a duplicate of this bug. ***
samba-3.0.20-r1 in portage