Pearltrees.com is a new service I discovered from the helpful folks on Bagcheck.com. It's a social bookmarking site that allows you to visualize your web bookmarks as "trees." The UI allows you to drag and drop your bookmarks and organize them into trees. It then allows you to discover and connect to related trees created by other users. I haven't used the site long enough to form an opinion on its utility, but it sure is fun to play with. Here's a pearltree I created for my UI pattern bookmarks.