Dinah, agreed. I am finding quite a few libraries are having their patrons tag their books they are interested in and ones they have checked out. The barrier that librarians have held up against tags has been crumbling as they are finding tagging a means to add to their metadata from perspective of the people they are trying to connect with.The formal structure and informal work really well together.It is important to remember/understand people tag for many different reasons. One is to categorize, others are just hooks for aggregating, some building their own collections (person tagging a DVD with DVD could be tagging for this reason), missing metadata, emergent terms, etc.