This thing was all about using the social bookmarking site delicious. First I checked out the CommonCraft video, which made it all clear. Then I watched the 8-minute podcast by a monotone Learning 2.0 narrator. It provided more in-depth info, but I found myself frequently checking to see how much time was left!
Then came visiting the site itself. It is amazingly easy to use. Its front page features the most recently bookmarked sites. I could see how these would be a potential time waster/distraction from your original focus! I already clicked on an article about the Marines starting a one-year ban of social networking sites (e.g. Twitter and Facebook), and one about the pardon of 2 American journalists in North Korea!
Every tag you choose or think up is like a differently-shaped funnel through which you can filter the internet's myriad websites. Not only that, you can see how many users chose the same tag for a certain website, who they are, and what other tags they chose for that site! And, on top of that, you can see all the other sites that they bookmarked. (This last feature would make me cautious of what I bookmarked on delicious and what I just bookmarked on my own computer!)
The networking feature is really cool. I can see it being useful in a class, maybe for a group project. However, I don't know that finding sites containing a particular tag and bookmarking them demonstrates an in-depth knowledge of a certain topic...but maybe you could then discuss the class network's findings together, and get the kids talking about why they chose this or that site, something new they learned on it, etc.? Or maybe the class network could be the first step for an individual research project? Like, you all find resources, discuss and choose the best sites, and then the kids proceed on their own from there? Hmmm... let me know if you have other ideas for classroom application!