Although Diigo is more complete than regular social bookmarking sites and I truly like the toolbar, introducing it to my friends doesn’t mean they’ll necessarily be blown away by it. I know some of them don’t even use Delicious, or have any way to back up their bookmarks so they still keep them in long folders on their browsers. In other words, a full client like Diigo is just too much for them. For simpler annotating, I’ve found SharedCopy to be light and simple, particularly because all of its features are presented in no more than a bookmarklet.
SharedCopy Lets You Bookmark & Annotate Websites With Style