SharePoint 2010 Standard Edition
SharePoint 2010 Enterprise Edition
SharePoint 2010 Online (Office 365 Edition)
It requires you to be logged in and have read access but no other privileges are necessary.
If there are tags or notes on a page, the Tags and Notes icon on the top right-hand corner of the page turns red. To review the information, click on the icon.
The Tags and NoteBoard dialog is displayed. You can review the tags that other users have left on the page.
To switch to the notes view, click on the Note Board.
Tags help you find pages again or classify the information that they contain. Notes are public comments that you leave on the pages for others to see. Use notes to add to the content, to correct any obvious mistakes, or explain information that is unclear. Don't use notes for observations such as "the author of this page is obviously a blithering idiot" unless you are confident that you can defend your viewpoint to the Managing Director without getting fired.
Creating and accessing my My Site
Tagging a SharePoint page so I can find it again later
Performing a basic search, Chapter 6