I have developed a different vision for a client of mine on a Comment and Note Taking functionality. This is the excerpt (building upon rating):
Comments and sticky notes
The system as it has been described so far allows the user to give a rating to another user and the link a user build up with other users. This information, though statistically valuable, has the drawback that no additional explanation is available for the reasoning behind this rating. Therefore public comments on ratings need to be possible as well.
Public comments on ratings and users have the drawback that they do not allow the user to attach a simple note to a contact. A simple note could e.g. be a reminder where and how you met this person, or additional information that you know about this person, which he neglected to put live on the website. As this information should not be made available to the public, we differentiate the public comment system from this sticky note taking system.
At times you might want to share your note with your colleagues. The managers should be able to view comments on people like „has two kids and wants them to join Hardvard“ from their predecessors. With the high turnover within the organisation, this note taking method allows for easy free form knowledge storage and retrieval over the years and across managers. Therefore it must be easy to give other parties (users, groups, roles) access to your personal notes.
A further enhancement of the note taking as well as commenting system is the ability not only to comment and rate on an object per se (e.g. a user), but also on parts of the information he has given. This idea of comments on part of the displayed content has been played with and experimented very successfully in the area of E-Learning. Blackboard e.g. allows users to mark certain passages within a document that is displayed in the browser and leave a comment or personal note. Flickr (http://flickr.com) on the other hand allows you to mark areas on a picture for comments (http://www.flickr.com/photos/ha112/901654/ ). This allows e.g. medical images to be presented to students while allowing them to mark notes on them (e.g. "In this area you can see the cancer starting").
Obviously public comments should allow a threaded discussion.
