Not only researchers, or known friends, but also strangers with same interest can make use of (rather exploit) this tool and do wonders. Say for example a bird watching community is on the prowl for a rare bird, or the very famous Flamingos, they all land up in a page that has abundance of information about the Flamingos, they can mark certain text in the page and leave a comment. Say a professor is leaving a comment about the Flamingos, and their migratory pattern, the others can see this note, respond to it! Later people with the same tool (Diigo toolbar) come to the page can see the conversation that has happened on the web, and note that this page is quite popular.