It's May and that means a new version of OpenBSD is out. My SNMP MIBs have been updated for 5.1 and are available for download on the OpenBSD SNMP MIBs page.
THIS WILL BE ONE OF THE LAST RELEASES OF THE MIBS FOR NET-SNMP.
During the OpenBSD 5.1 development cycle, I committed the CARP MIB to the base OpenBSD snmpd. The kernel sensor MIB has been in the base snmpd for a few releases now. That leaves the pf MIB which was committed to 5.1-current some weeks ago and will be present in the 5.2 release.