A new Google Toolbar feature allows web users to read and comment on any and every web site they visit. Google Sidewiki appears as a browser sidebar, where you can read and write entries along the side of the page.
The new feature available for the Firefox and IE versions, but not for Google chrome

.One can download it from
http://www.google.com/sidewiki. The new tool is somewhat similar to Yahoo's online note-taking tool, Searchpad. Unlike in direct comment posting, where there is no organized way in which entries appear, Sidewiki has a ranking algorithm to place most relevant comments first.