Finding it on Google, finding it on del.icio.us

We consider search engines and collaborative tagging systems from the perspective of resource discovery and re-finding on the Web. We performed repeated searches over nine months on Google and del.icio.us for web pages related to three topics selected to have different dynamic characteristics. The results show differences in the resources they provide to the searcher. The resources tagged on del.icio.us differ strongly from the top results returned by Google. The results also suggest the changes in the most recently tagged web pages may be associated with the level of activity in user communities and, indirectly, with external events.