Seattle-based Blue Dot has rolled out a new service, saying last night that it has launched "Blue Dot Buzz", a new ranking service that shows the most popular topics tagged by the company's users. Blue Dot provides a social bookmarking service that allows users to share web pages with other users. The new service now shows the most popular post topics on its home page, along with a tag cloud of popular posts. The service also allows users to see the most popular posts on particular topics.