1. Stumble Upon

I have seriously been contemplating a topic switch from Vanilla for several weeks and have finally decided to do so. There are a number of reasons behind this but, namely, Vanilla didn't provide a visually representative enough tool without having to do intense configuring. Therefore, I am swtiching over to a super cool program called StumbleUpon.
StumbleUpon is a website and content discovery service enabled by a browser toolbar. StumbleUpon uses positive and negative user ratings to form collaborative opinions on website quality. When users stumble, they will only see pages which friends and like-minded stumblers have recommended. More often than not, it’s something almost serendipitously interesting to the reader. Apparently, the company expanded into video discovery in late 2006 (I'm exploring these capabilities right now).
As I've been looking around on different blogs (stumbling, as it were) people who are passionate about StumbleUpon say they like it because of the surprise factor in what they see next, and the fact that the product has such a high hit rate in delivering interesting new content. The StumbleUpon site says they have nearly 7.5 million users as of April, 2009, up from 1.7 million in December 2006. Over 15 million personalized recommendations (“stumbles”) are delivered daily.
StumbleUpon was acquired by Ebay in May 2007, and operated as an independent subsidiary for 2 years. In April 2009, StumbleUpon was bought back from Ebay by Garrett Camp, Geoff Smith, Ram Shriram, Accel Partners and August Capital.
http://www.stumbleupon.com/

StumbleUpon, as I've discovered, is a cool place to discover content that matches your interests. It's important to remember, though, that all these cool and interesting sites you Stumble were actually submitted by users who share your common interests!
Just as you enjoy discovering new sites, you can also discover new people on StumbleUpon. StumbleUpon has features that make it easy to connect and share sites with others, learn more from them and ultimately find well-informed users and sources in your particualr areas of interest.
Meeting similar Stumblers is fun and useful. From a librarians point of view, one can utilize StumbleUpon to conduct research, collect data for a project or presentation or look for experts in library-related topics that interest you. StumbleUpon just published a tutorial aimed toward helping users Discover Similar People on StumbleUpon.
Enjoy!
Sources:
StumbleUpon. (2009) About us. Retrieved from http://www.stumbleupon.com/aboutus/
StumbleUpon. (2009) Recommendation technology. Retrieved from
http://www.stumbleupon.com/technology/