I find it helpful by creating a list that searches for all un-tagged items.
e.g. Searched for: (status:incomplete) NOT (isTagged:true)
Since I focus mainly on lists, I create another smart list to find items that were tagged but not in my lists.
e.g. (tag:## OR tag:#) NOT (list:$$ OR list:$$$)
Posted at 9:45pm on March 19, 2013