This has been mentioned here before, but I thought it was cool the explanation Webster Cash gave for it in the video on this TV news site:

CU Researcher Invents Star Shade To Study Planets.
Shaun Boyd
Reporting
"(CBS4) BOULDER, Colo. A researcher at the University of Colorado in Boulder is getting international attention for his invention that helps scientists find never-before-seen planets and map their make-up."
...
"If we can find planets similar to Earth and actually chemically analyze what's going on in their atmospheres, we may be able to for the first time take a look at alien life," Dr. Cash said.
"The hope is to build and launch the star shade within the next decade."
http://cbs4denver.com/topstories/local_story_186222050.html

Other links on it:

Starshade brings fresh hope in search for alien life.
By Roger Highfield, Science Editor
Last Updated: 12:55am BST 06/07/2006
http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2006/07/06/wspace06.xml

Ultradeep occultation for planet hunting.
Cash, Webster
http://newsroom.spie.org/x4194.xml?highlight=x541

Detection of Earth-like planets around nearby stars using a petal-shaped occulter.
Webster Cash
Nature 442, 51-53 (6 July 2006) | doi:10.1038/nature04930; Received 16 January 2006; Accepted 19 May 2006.
http://www.nature.com/nature/journal/v442/n7098/abs/nature04930.html [abstract only]

Bob Clark