What a great list! I've had fun going through the list. I did not go through each one, but basically picked the ones that "caught my eye" so to speak. When I went to Furl, the site for Diigo came up. I use Diigo for social bookmarking. As expressed before in one of my other entries I stated that I really like using Diigo. I love, love Library Thing and have had a good experience working with Google Docs. I recently was introduced to Biblio when I was cataloging some videos, but never really got the chance to delve into it. WorldCat was interesting. When I typed in a search for a book, it listed local libraries that had the book and citations were also available. This is one that I might use quite often. Lulu had a "Rare Book" section that was interesting as well. Could be used to locate books no longer in print. I liked Yourminis for widgets.
As for my personal use I had such fun and laughed and laughed when I explored with HairMixer. My sisters would love this one. Since I am a music fan and seem to always get the lyrics wrong, I had fun with Last.fm and LyricsMode. When my nephew was looking for a home he introduced me to Zillow and I have been using it ever since.