AIX 5.2 and 5.3 install pioinit with user and group ownership of bin, which allows local users with bin or possibly printq privileges to gain root privileges by modifying pioinit.
http://www.vupen.com/english/advisories/2007/2678
http://www-1.ibm.com/support/docview.wss?uid=isg1IY79786
http://www-1.ibm.com/support/docview.wss?uid=isg1IY79785
http://securitytracker.com/id?1018468