Make adding keywords (aka "tags") easier

I think a great feature would be to add special pop-up window that allows the user to add to the list of keywords, or “tags”. Tags are a very popular way of organizing information: for example, the Delicious bookmarks resource make extensive use of tags, as does the Windows 7 file explorer. The new feature would work by allowing the user to right-click on a reference, or use a keyboard shortcut to generate a pop-up window that shows the current list of keywords for that reference, and then these could be edited in that window.  This would save a great deal of tme over the method of opening the reference and navigating to keywords (by the way, arrow keys or page up/down would be a logical addition to the tab key for moving between fields). Using keywords with smart groups is a powerful organization feature.  I organize about 300-600 references per week, and smart groups + keywords is a huge help, espcially with the new PDF search mechanism.