One aspect relates to a social bookmarking system that has the capability of displaying advertisements based on user input provided to the system. Advertisements displayed to the user may be determined based on one or more classifications provided by the social bookmarking system and selected by the user. Further, classification information that is created, used, or otherwise associated with the particular user may be used to determine ads displayed to that user. Another aspect relates to a system for collecting user classifications of content and using such classifications to match ads to appropriate content. In such a manner, more appropriate associations between ads and content may be made. Such classifications may be collected, for example, using a social bookmarking system. Further, advertisers may subscribe to classifications created in the social bookmarking system, allowing their advertisements to be displayed to users that perform actions with the subscribed classification. Also, advertisers may be permitted to submit their own classification information to the social bookmarking system.