Twine is a semantic web version of del.icio.us.
I've got a few invites floating around. Be aware, it's a real beta - that means rough around the edges.
At first, you might not see the value in it, at least not until you peek under the hood - every item you add is exportable as RDF.
The other side of that is like del.icio.us recommending what other people have tagged an item with, Twine will recommend related or similar items, based on picking out common people, themes, etc.
If you'd like to see, drop me a line.