StumbleUpon is an Internet community that allows its users to discover and rate Web pages, photos, and videos. It is a personalized recommendation engine which uses peer and social-networking principles.
Web pages are presented when the user clicks the "Stumble!" button on the browser's toolbar. StumbleUpon chooses which Web page to display based on the user's ratings of previous pages, ratings by his/her friends, and by the ratings of users with similar interests. Users can rate or choose not to rate any Web page with a thumbs up or thumbs down, and clicking the Stumble button resembles "channel-surfing" the Web. StumbleUpon also allows their users to indicate their interests from a list of nearly 500 topics to produce relevant content for the user.There is also one-click blogging built in as well.