Any one who is familier with Wikipedia ( http://en.wikipedia.org/wiki/Main_Page ) and enjoys the service should enjoy the new Mozilla Firefox extention Wikalong ( http://www.wikalong.org/ ). This program installs a side bar on your Mozilla web browser that allows you to view others' comments on a web page as well as edit the content of the side bar to include your own input. "See also" references, critiques and comments are two possibilities that make this tool more than worth the time it will take to download and learn the basics. One of the greatest parts is that it is totally free of charge and advertisements.
Get Firefox at http://www.mozilla.org/products/firefox/