Diigo has gained a pretty significant following among educators as an alternative to Delicious because you can do more with it. If you’re new to Diigo, it’s a free social bookmarking software that comes as an extension to your browser (e.g., Firefox). In addition to tagging and creating groups, you can annotate pages with stickies, find other users via public annotations, tweet bookmarked pages, create lists, as well as various other things. So, if an instructor would like to have students do more than just passively read web pages, a tool like Diigo stands out as a good option.
On the new feature front, I recently found out that they’ve got a WebSlides option that makes it extremely easy to string together a series of web pages and present them to a class or group. One way to quickly create a slideshow is to select a list from your Diigo collection and then click the slides widget. Another option is to create them directly from an RSS feed. In true Web 2.0 fashion, viewers can also become participants by annotating the slides. Especially for people teaching online, this would be another way for both teacher and students to generate interactive discussions about web-based materials. It also has other options which you can check out from Diigo’s intro video.