There are two ways for selecting tags. One is the drop down menu and the other is displaying them in the top nav area. The first way, the drop down menu doesn't give you an indication that any item is applied. It's something we we've heard about before and hopefully will have time one day to indicate a tag is applied.
The other way is to click the triangle next to the tag drop down menu. The displays all areas and tags and allows you to quickly select and deselect areas and tags. Areas and Tags that are selected are shown in yellow.
It sounds like this mode would be best for your purposes. Thanks!