Social bookmarking has emerged as a growing source of human generated content on the web. In essence, bookmarking involves URLs and tags on them. In this paper, we perform a large scale study of the usefulness of bookmarked URLs from the top social bookmarking site Delicious. Instead of focusing on the dimension of tags, which has been covered in the previous work, we explore social bookmarking from the dimension of URLs. More specifically, we investigate the Delicious URLs and their content to quantify their value to a search engine. For their value in leading to good content, we show that the Delicious URLs have higher quality content and more external outlinks. For their value in satisfying users, we show that the Delicious URLs have more clicked URLs as well as get more clicks. We suggest that based on their value, the Delicious URLs should be used as another source of seed URLs for crawlers. Categories and Subject Descriptors H.3.3 [Information Search and Retrieval]: Search Proce...