There's also a very nice new browser sidebar that shows you a lot of very useful and focused information, including your own latest bookmarks, those from your Diigo friends, and most cleverly, the Diigo users who have also saved information from the page you're visiting as well as the site itself.
I recommend Diigo, especially with the plug-in. It's a complex tool but if you take a few minutes to learn what it can do and how it does it, it can make you a more productive, smarter Web user.