I think I used it in the days before Yahoo had bought it and then you had to register to view the bookmarks. I wanted to create links for our library users but abandoned it when the bundling into groups didn't really work and people had to register to use. Now it looks much improved and I will definitely set up a library account and start developing links online. Delicious was my first experience of non-controlled language for tagging, which I thought would never work as the same resource had lots of different tags. But now it has expanded and more keywords are in the system it seems to work well. Plus if I am bundling items together I can ensure that they have consistent tags.
Certainly a thing that I am going to try again and use directly to help our library users.