Diigo is a so called "second generation" social bookmarking site. It adds a lot of other functions (like annotations on websites) but most importantly for me it adds groups. Diigo Groups once joined will send you an email containing the links saved by the group for that day/week. I have joined several of these groups and find them a constant source of new and interesting information.
Here is a shot of the summary of the Diigo in Education group which is the most active of the groups I have joined.
As you can see there are 1561 bookmakrs and 1744 members.
If you can handle a couple of extra emails in your inbox every couple of days then be sure to check out Diigo Groups and subscribe to them.
Social bookmarking was first made famous by Del.icio.us which was a simple way to save your bookmarks on the web by "tagging" them with single words that help catagorize them. You can share bookmarks between many computers and have access to your bookmarks on any computer. Here is where it gets interesting... You can share your bookmarks makeing them appear on your web page (RSS Feeds) or inside anyone's web browser (live bookmarks in Firefox)
What makes social bookmarking more interesting is the opportunity to browse other people's bookmarks and see what links have been saved by people who share your interests.
Here there are 318 other people who have bookmarked the same page on Moodle.
I can click the green number and be taken to a page that shows the others in a list.
simoes.pg is another user with 24 Moodle bookmarks that I can visit.