Would be nice to have the parameters "log_format", "log_time_format" for determine customized format of debug log for zabbix daemons.
Now the log records start from:
21300:20110930:175341.220
and it's not so easy to read them.

Suggested value for parameters:
log_format=%T %L zabbix_server[%P] %M
log_time_format=YYYY-MM-DD HH:MM:SS
Where:
%T - formant of data/time,
%L - message level ?
%P - PID,
%M - text of message.

Then, the line:
19128:20110929:152540.796 Starting Zabbix Server. Zabbix 1.8.8 (revision 21965).
will be like this:
2011-09-29 15:25:40.796 INFO zabbix_server[19128] Starting Zabbix Server. Zabbix 1.8.8 (revision 21965).

Why?
Most often, when viewing the debug log, you need determine when the event was occurred and the line beginning with "2011-09-29 15:25:40.796" much easier readable than the line beginning with "19128:20110929:152540.796".