Great example of how social bookmarking can be used with students so they can find and save information. A very useful feature is the private or public Groups, which can be based on a grade level or unit of study. 

Once a site is bookmarked in Diigo, it can be shared in a variety of ways. Below, my latest "PLN Gems" are shared using the RSS gadget. I have been using Diigo since 2007. My first foray into cloud-based booking was with Blogmarks and Delicious in 2004.