PUBLIC MARKS with tags semtags & flickr

We are rolling out a new feature called "machine tags" that allows users to be more precise in how they tag, and how they search, their photos.

Tags have taken the internet by storm. Where once the question was “what are they,” now all people want to know is whether a given site offers them. But what are the actual benefits of tags? What motivates millions of Flickr, del.icio.us and blog users to add tags to their photos and posts? And what is it about tags and tagging that gets information architects and user experience professionals so excited?