Check out the cool Firefox browser extension, Blue Organizer, from Adaptive Blue . It was launched at the September 2006 DEMO  conference.
A TechCrunch  blog entry provides an indepth look at products introduced at DEMO. Of Blue Organizer, it says "combines its own ontology with your tags, lets you perform a very long list of functions with each item you’ve saved and does a lot of smart little things like gleaning tags from topical databases and bookmarking pages automatically once you’ve visited them three times. Social bookmarking is a crowded space, but for people who seek a well constructed tool that balances an intuitive user experience with features to please the power user, Blue Organizer may be a very good option. The beauty is in the details in this one."
I agree about the details. Even if it doesn't appeal to you, check out the interactive tutorials  for good online learning examples.
If you just have time for a quick peek at new social networking offerings, see this PC Magazine article .