I don't use tags or multiple notebooks at all. Instead I use keywords in the titles of all my notes. Here are some example note titles: myco - TODO = my TODO list at My Company, where I work. myco - proj1 - mtg notes = all my meeting notes about Project1 at My Company. myco - proj1 - work notes = my ongoing work notes about how I'm implementing Project1. etc... Then I have a saved search for "intitle:myco". I click on that, then I can do a "intitle:proj1" search to get just myco / proj1 notes. Doing a search after clicking on a saved search will search only within the saved search results so it's kind of like a refined search.