If you are like me, someone who forgets why he bookmark a site the next day, you will find this feature handy. If I look back on my del.licio.us page, I can’t remember why I bookmarked half of the site on it.
This I think is going to be really useful for collage student, when they are researching something on the web. They could put annotation on sites they found and share then with their other buddies in Diigo.
Having Diigo lets you access another world of the web. You will see public highlights of sites by other Diigo users. There are 3 view modes, all (view all highlights and stickies), private (view only your highlights or stickies) and disable (no view of any highlights or stickies).
Same like other social bookmarking services out there, you can subscribe / watch what other people are bookmarking. In Diigo, you can subscribe to a person or a tag and there is this mail looking icon on the Diigo toolbar in your Firefox that will show new bookmarked sites either by someone or some tag you subscribed to.