Cathy Marshall, a senior researcher at Microsoft, conducted a short study on the effectiveness of using tags to describe content. The article, "Do Tags Work?" is a bit lengthy (and needs editing), but the findings basically show that people generally don't use verbs when tagging and that the titles and descriptions they write are almost always a more useful definition of the thing being tagged (especially when searching across large datasets). The tags are, if anything, only useful to the tagger himself (and even then, time is likely to erase from memory the words he would have used since the tags most likely did not contain verbs).