When compiled with USE=-tcpd snmpd (from package net-snmp) is unable to accept connections, even locally when you already have ALL: localhost in /etc/hosts.allow More details at: http://sourceforge.net/mailarchive/forum.php?thread_id=1354970&forum_id=7153 and http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=145088&repeatmerged=yes net-snmp should not honor the -tcpd USE flag
do patches in http://sourceforge.net/tracker/index.php?func=detail&aid=550830&group_id=12694&atid=312694 fix it for you?
last comment in http://sourceforge.net/tracker/index.php?func=detail&aid=550830&group_id=12694&atid=312694 says they will be applied after 5.0.1. All gentoo versions are above this. Therefore the bug isn't valid cause they should of been fixed. Please reopen if this is not the case.