I have been using Stumbleupon for some time. It is quite interesting site. If you have some free time and want to just suft. It is the best place. You can choose the topics of your interest. Stubleupon will throw you some new sties (with high rating) when u click the stumble button. You can rate the site using 'I like it' or 'dont like it'. When u click 'i like it' it automatically added to ur favourties.
These kind of services (web 2.0) are the new trend in Internet. It is quite powerful especially in the new era of information overloading. For each kind of requirement there are n number of sites available. It is impossible to evaluate each one and choose the best. These kind of syndication tools provide very good rating mechanism. However I am not very sure if it is tamper proof. How about if the provider tampers the ratings. If the ratings are tampered heavily then credibility may be lost. However if they tamper only to certain extend then you may not notice it. Another approach is like google putting advt as separate list. this is not very effective as nobody will click on the advt (it is not only displaying your name in the screen, but also about credibility). God knows if the providers really tamper the list or not.