onPostModify Is there a way to retrieve a list of all attributes that were NOT modified?

The $Request only contains changes.  The simplest way to obtain the pre-change values is to do a Get-QADUser within your PreModify handler as you have been doing.

All right. I was hoping for an approach where I could prevent running a get-qaduser. 
Thanks for your reply. 

I did something similar but it was just for simple logging. 

On PreModify Get the value and use an In Control (it's a way to store data through a request)

$request.PutInControl("PreMoveDN", $DSTYPE_CASE_IGNORE_STRING, $Request.DN )

Then after the request starts, OnPostModify for example you can get the control value

$OriginalLocation = $request.GetInControl("PreMoveDN")

Now you can compare

If($OriginalLocation -ne $NewLocation){do your magic}

################################################
if you want to do a list of attributes, I keep a list and start out like this:

#Go through list of attributes and add them to the $Request 
foreach($Attribute in $Request.Attributes.Attributes.Name)
{

try
{

#Get the existing value of the Attribute
$Value = $DirObj.get($attribute)
........ to the end of whatever...

Maybe too much info, but worth a shot. 

That sounds like a great alternative. I think I will give it a try !

Following JohnnyQuest's response, I took to approach of using get-qaduser to obtain the original values. I was just worried that the command would be "costly" in terms of IO but limiting the number of returned attributes with "-IncludedProperties" seams not too bad.

Thanks for your response 

The $Request only contains changes.  The simplest way to obtain the pre-change values is to do a Get-QADUser within your PreModify handler as you have been doing.