What's the most useful custom field that you've added to RT?

On our RT instance, we have three custom fields that work well in unison

The first is Component which helps to categorize support issues

Then we have a pair called Question and Answer. If a ticket can be summarized into a question and answer a few lines long, staff are encouraged to fill out the question and answer section of the ticket (I have question and answer grouped as ‘Q and A’ using CustomFieldGroupings ).

I then have a saved search for all tickets where Question is not NULL, ordered by Component. This is an excellent way to find quick answers in the ticketing system.

Does anyone else have interesting, creative and useful custom fields?