http://www.codenotes.com/articles/articleAction.aspx?articleID=1908
Example and Explanation on String Builder Class
A picture say's more than the words, Jeff's article puts an image which clearly distinguish the mutable and immutable objects with example's, here it follows
http://www.dotnetjunkies.com/Tutorial/60C1B927-8F55-4F4B-B050-48E693757E05.dcik
Thanks Jeff for the link..