"Just looking at an object, and seeing other tags at the same time is extremely addictive. You can quickly jump to and fro within this kind of taxanomy with little effort. With certain experiments, we've seen a user stickyness not noticed before. And using RSS to monitor a tag is a great way to keep updated on content that you're really interested in.

... I suspect we'll all see a large group of sites dedicated to tagging almost anything (books, products) that are more specific and open to finding a small but vocal niche of people."
  - in Social Bookmarking Services Revisited at slashdot (написанной по причине выхода статьи Social Bookmarking Tools.)