Caching pages is useful for those sites that, for instance, require passwords to gain access to. With the cache (or snapshot) feature, Diigo captures a "photograph" of a page for any user who is able to access the page through a password. This snapshot may then be shared so that even those without password access may view the page. This is just one example use of caching, and there are other uses as well.

There is a neat solution to the caching problem and it can be found at http://groups.diigo.com/group/Diigo_HQ/content/almost-perfect-solution-to-caching-problem-icyte-1889535 .

Learn from experts in different fields through video interviews. Quite similar to TED. Great resource.

Some of my students are very proficient readers whereas others are very far from that. In our group page, bookmarks to readings are tagged with a number from 1 (very easy) to 5 (very challenging). This gives students a rough guide about the difficulty level of the texts. It also allows me to assign different readings to different students, roughly according to their reading proficiency levels.