I just upgraded my 1.6.6 server to 1.6.7. After a few seconds, i noticed this in my processlist:

zabbix 11807 0.0 0.0 86608 2532 ? SN 17:17 0:00 /usr/sbin/zabbix_server
zabbix 11814 0.7 0.0 0 0 ? ZN 17:17 0:06 [zabbix_server] <defunct>
zabbix 11815 0.4 0.0 0 0 ? ZN 17:17 0:03 [zabbix_server] <defunct>
zabbix 11816 0.7 0.0 0 0 ? ZN 17:17 0:06 [zabbix_server] <defunct>
zabbix 11817 0.4 0.0 0 0 ? ZN 17:17 0:03 [zabbix_server] <defunct>
zabbix 11818 0.6 0.0 0 0 ? ZN 17:17 0:05 [zabbix_server] <defunct>
zabbix 11819 0.5 0.0 0 0 ? ZN 17:17 0:04 [zabbix_server] <defunct>
zabbix 11820 0.7 0.0 0 0 ? ZN 17:17 0:06 [zabbix_server] <defunct>
zabbix 11821 0.4 0.0 0 0 ? ZN 17:17 0:03 [zabbix_server] <defunct>
zabbix 11822 0.7 0.0 0 0 ? ZN 17:17 0:06 [zabbix_server] <defunct>
zabbix 11823 0.4 0.0 0 0 ? ZN 17:17 0:03 [zabbix_server] <defunct>
zabbix 11824 0.6 0.0 0 0 ? ZN 17:17 0:05 [zabbix_server] <defunct>
zabbix 11825 0.4 0.0 0 0 ? ZN 17:17 0:03 [zabbix_server] <defunct>
zabbix 11826 0.6 0.0 0 0 ? ZN 17:17 0:05 [zabbix_server] <defunct>
zabbix 11827 0.4 0.0 0 0 ? ZN 17:17 0:03 [zabbix_server] <defunct>
zabbix 11828 0.7 0.0 0 0 ? ZN 17:17 0:06 [zabbix_server] <defunct>
zabbix 11829 0.4 0.0 0 0 ? ZN 17:17 0:03 [zabbix_server] <defunct>
zabbix 11830 0.0 0.0 0 0 ? ZN 17:17 0:00 [zabbix_server] <defunct>
zabbix 11831 0.0 0.0 0 0 ? ZN 17:17 0:00 [zabbix_server] <defunct>
zabbix 11832 0.0 0.0 0 0 ? ZN 17:17 0:00 [zabbix_server] <defunct>
zabbix 11833 0.0 0.0 0 0 ? ZN 17:17 0:00 [zabbix_server] <defunct>
zabbix 11834 0.0 0.0 0 0 ? ZN 17:17 0:00 [zabbix_server] <defunct>
zabbix 11835 0.1 0.0 0 0 ? ZN 17:17 0:01 [zabbix_server] <defunct>
zabbix 11836 0.1 0.0 0 0 ? ZN 17:17 0:01 [zabbix_server] <defunct>
zabbix 11837 0.1 0.0 0 0 ? ZN 17:17 0:01 [zabbix_server] <defunct>
zabbix 11838 0.1 0.0 0 0 ? ZN 17:17 0:01 [zabbix_server] <defunct>
zabbix 11839 0.0 0.0 0 0 ? ZN 17:17 0:00 [zabbix_server] <defunct>
zabbix 11840 1.3 0.0 0 0 ? ZN 17:17 0:11 [zabbix_server] <defunct>
zabbix 11841 0.4 0.0 0 0 ? ZN 17:17 0:04 [zabbix_server] <defunct>
zabbix 11842 0.0 0.0 0 0 ? ZN 17:17 0:00 [zabbix_server] <defunct>
zabbix 11843 0.0 0.0 0 0 ? ZN 17:17 0:00 [zabbix_server] <defunct>
zabbix 11844 0.0 0.0 0 0 ? ZN 17:17 0:00 [zabbix_server] <defunct>
zabbix 11845 0.0 0.0 0 0 ? ZN 17:17 0:00 [zabbix_server] <defunct>

Setting DebugLog to 4 and restarting the server eventually lead me to this:

13408:20091116:173402 oid_index:ifDescr
13409:20091116:173402 End update_triggers [53404]
13397:20091116:173402 In evaluate_function('web490:proc.num[syslogd].last(0)')
13408:20091116:173402 index_value:ge-4/0/42
13411:20091116:173402 End update_functions()
13405:20091116:173402 End update_functions()
13409:20091116:173402 Query [commit;]
13408:20091116:173402 In snmp_normalize(oid:ifDescr)
13411:20091116:173402 In update_triggers [itemid:163806]
13405:20091116:173402 In update_triggers [itemid:169688]
13408:20091116:173402 End of snmp_normalize():1.3.6.1.2.1.2.2.1.2
13411:20091116:173402 Query [select distinct t.triggerid,t.expression,t.description,t.url,t.comments,t.status,t.value,t.priority,t.type from triggers t,functions f,items i where i.status<>3 and i.itemid=f.itemid and t.status=0 and f.triggerid=t.triggerid and f.itemid=163806]
13405:20091116:173402 Query [select distinct t.triggerid,t.expression,t.description,t.url,t.comments,t.status,t.value,t.priority,t.type from triggers t,functions f,items i where i.status<>3 and i.itemid=f.itemid and t.status=0 and f.triggerid=t.triggerid and f.itemid=169688]
13408:20091116:173402 In cache_get_snmp_index(oid:1.3.6.1.2.1.2.2.1.2,value:ge-4/0/42)
13384:20091116:173402 One child process died. Exiting ...
13408:20091116:173402 End of cache_get_snmp_index(index:0):FAIL
13402:20091116:173402 End update_functions()
13408:20091116:173402 In snmp_get_index(oid:1.3.6.1.2.1.2.2.1.2,value:ge-4/0/42)
13400:20091116:173402 Got signal. Exiting ...
13401:20091116:173402 Got signal. Exiting ...
13402:20091116:173402 Got signal. Exiting ...
13417:20091116:173402 Got signal. Exiting ...
13416:20091116:173402 Got signal. Exiting ...
13419:20091116:173402 Got signal. Exiting ...
13425:20091116:173402 Got signal. Exiting ...
13397:20091116:173402 Got signal. Exiting ...
13421:20091116:173402 Got signal. Exiting ...
13426:20091116:173402 Got signal. Exiting ...
13428:20091116:173402 Got signal. Exiting ...
13414:20091116:173402 Got signal. Exiting ...
13411:20091116:173402 Got signal. Exiting ...
13399:20091116:173402 Got signal. Exiting ...
13418:20091116:173402 Got signal. Exiting ...
13407:20091116:173402 Got signal. Exiting ...
13424:20091116:173402 Got signal. Exiting ...
13422:20091116:173402 Got signal. Exiting ...
13406:20091116:173402 Got signal. Exiting ...
13427:20091116:173402 Got signal. Exiting ...
13415:20091116:173402 Got signal. Exiting ...
13405:20091116:173402 Got signal. Exiting ...
13413:20091116:173402 Got signal. Exiting ...
13420:20091116:173402 Got signal. Exiting ...
13423:20091116:173402 Got signal. Exiting ...
13403:20091116:173402 Got signal. Exiting ...
13410:20091116:173402 Got signal. Exiting ...
13408:20091116:173402 Got signal. Exiting ...
13404:20091116:173402 Got signal. Exiting ...
13409:20091116:173402 Got signal. Exiting ...
13412:20091116:173402 Got signal. Exiting ...
13384:20091116:173404 Query [SET CHARACTER SET utf8]
13384:20091116:173404 In free_database_cache()

Not sure if anything useful is inthere, but that's as far as i got.
Reverted to 1.6.6 now and everything is fine again.