Plist in /System/Library/LaunchAgents not loading on reboot
Is the property list owned by root? If it is not, it is not loaded on login even if launchctl load (without sudo) would load it.

$ sudo launchctl load /Library/LaunchAgents/test.plist 
launchctl: Dubious ownership on file (skipping): /Library/LaunchAgents/test.plist
nothing found to load
$ sudo chown root /Library/LaunchAgents/test.plist 
$ sudo launchctl load /Library/LaunchAgents/test.plist 
$ 


If the program is meant to be run when the property list is loaded, set RunAtLoad to true:

&lt;key&gt;RunAtLoad&lt;/key&gt;
&lt;true/&gt;


Also you can normally use /Library/LaunchAgents/ instead of /System/Library/LaunchAgents/. From man launchd:

~/Library/LaunchAgents         Per-user agents provided by the user.
/Library/LaunchAgents          Per-user agents provided by the administrator.
/Library/LaunchDaemons         System-wide daemons provided by the administrator.
/System/Library/LaunchAgents   Per-user agents provided by Mac OS X.
/System/Library/LaunchDaemons  System-wide daemons provided by Mac OS X.