The main thing to remember about duty officers is that they:
--modify your own skills
--can be sent on mini-missions on a regular basis
Duty Officer Guides
Duty Officers 101:
http://forums.startrekonline.com/showthread.php?t=220296
Doffs for Doofuses:
http://forums.startrekonline.com/showthread.php?t=233726
Duty Officer Overview:
http://www.stowiki.org/Duty_officer
Duty Officers, A Recruitement Guide:
http://forums.startrekonline.com/showthread.php?t=244318