i emerged postgres 7.2-r3 and the install script did not create a postgres user. this is missing. i create one by hand and now it is running. im not sure if postgres needs a /bin/bash in passwd. the "ebuild /var/db..../postgres config" needs one in order to run but postgres does not. i now have a line like "postgres:x:70:70:postgres:/var/lib/postgresql:/bin/false" in /etc/passwd.
committed