Agent can not use vfs.file.contents in versions 2.0.3 or 2.0.4rc1. I haven't tried any other version.

myhost/root/home/root/wrk/zabbix-2.0.4rc1/src/zabbix_agent)(root)#./zabbix_agent -t "vfs.file.contents[/etc/services]"
vfs.file.contents[/etc/services] [m|ZBX_NOTSUPPORTED]

This doesn't work in 2.0.3, but it does work in 2.0.3 on HP-UX.