Abandoning taxonomy is the first ingredient of success. These systems just use bags of keywords that draw from — and extend — a flat namespace. In other words, you tag an item with a list of existing and/or new keywords. Of course, that idea’s been around for decades, so what’s special about Flickr and del.icio.us? Sometimes a difference in degree becomes a difference in kind. The degree to which these systems bind the assignment of tags to their use — in a tight feedback loop — is that kind of difference.