Starting with verion 1.6.1, UserParameters with commas in the command don't work and prevent the agent from starting. The log file contains:
635:20090209:113247 zabbix_agentd started. ZABBIX 1.6.2.
635:20090209:113247 UserParameter "<key>,<command>" FAILED: Invalid format.
zabbix_agentd [635]: Wrong value of [UserParameter] in line 93.
zabbix_agentd [889]: Warning: ZABBIX semaphores already exist, trying to recreate.
Version 1.6.0 works fine. Commas are very useful for UserParameters with inline SQL.