Application and Session Variables and Locking

I have four CFCs that I would like to be available to all pages.  Initially, I was storing the CFCs in a session variable, but one of the exchange experts recommended that I store the cfcs in an application variable, partly to deal with my JRun (out of memory) situation.  I have made the changes, but now I am receiving a 500 null null error.  While trying to search for solutions on resolving the 500 null null error. I came across a couple of posts that say you should lock application and session variables.  I sort of understand the logic behind the locking, but I am not really clear whether it is an absolute must and when and how to use them.  The bloggers even said you should lock application/session variables even during reads.  I was locking my session variables but then I notice a drop in the performance of my application so I removed them.  So, I have the following questions:

1. How do you store a CFC in an application and reference (and or call) the methods stored in the CFC?  I think I am doing something wrong which is why I am receiving the 500 null null error message.  Please see code snippet to see my attempts.

2. If I need to modify a method in the CFC or add any new methods, will the changes be reflected in the application variable since the state of the lasts for as long as the application or would I need to restart the coldfusion server for the cfc to be updated with the new changes?

3.  Do I need to lock all session and application variables even when calling the CFC application variable to invoke (call) a function and even when passing session variables to a CFC function as arguments or querying the database?  Also what about outputting information stored in a session variable (ex. <cfoutput>Logged in #session.user_firstname# #session.user_lastname#</cfoutput>)

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Code for instanting cfc and storing it into application variable:
if(not isdefined("application.objSystem")){
  application.objSystem = createobject("component","System");
}
 
Code for calling method inside CFC application variable:
if(application.objSystem.listValuesFound(session.usergroup, "Instructor,System_Administrator")){
				menu = menu & '<li><a href="ViewCourses.cfm?#session.URLToken#">Create, View or Edit Courses</a></li> <br /><br /> #chr(10)##chr(13)#';
}