November 22nd, 2008 
“A lot of photographers capture motion simply to convey that an object is moving. But, there are other reasons to so. Movement can communicate mood. Trees rustling in the wind suggest serenity while throngs of people on a busy city block imply harried activity.”
An excellent article by digital-photography-school.com which covers the art of capturing motion, speed and blur in your photographs.
Read the article here