stumbleupon – Social networking for Web Surfing ?

www.stumbleupon.com
The pitch is that its an intelligent browsing tool for sharing and discovering great websites. As you use it, you’ll get high-quality pages matched to your personal preferences. These pages have been explicitly recommended (rated I like it) by other SU members with similar interests. In return, your rating of these sites shares them with your friends and peers ??” the theory is that you will automatically ‘stumble upon’ each others favorites sites.