First off, I love Salesforce, but don't you wish that Salesforce would just let you hit a record and ignore the fact that you, the System Administrator, edit the record so that metrics wont get skewed by your edits? Many sales & support managers monitor the Last Modified By field. But, they just dont like it when we push new function into the system and we are forced to do a mass update of 10,000 records. 

I'm sure Salesforce will resolve this issue in 10 years (safe harbor). Here is a really quick workaround to resolve this issue! 

1. Create a new text field field called: Last Modified By Name NonAdmin, dont put it on the page layout, make it read only.

2. Create a new datetime field called: Last Modified NonAdmin D/T, dont put it on the page layout, make it read only.
3. Create a new formula field called: Last Modified By NonAdmin and concatonate the previous two fields so you simulate the "Name Date Time" function.
4. Create a workflow that evaluates when the object system field LastModifiedById field is changed AND not the same as the logged in $user
4. Create a field update to stamp the D/T field with NOW()
5. Create a field update to stamp the Name NonAdmin with the $user's full name

This effectively allows no change to the Last Modified By NonAdmin field when a System Administrator hits the record. But, when anyone else edits it, boom, you get hit! When I get more time, i'll update this post to enhancing the logic and make the name portion a hyperlink to the user record.

Keep in mind, that any reports using the objects Last Modified By system field will need to be updated to use the new field/s accordingly. 

Hope this helps a few of you. 

For those of you who want the System Last Modified field to be able to dynamically ignore a specific profile, go vote on that idea: 

https://success.salesforce.com/ideaview?id=08730000000BrSKAA0