Optimizing Conversion Rates: It's All About Usability | How-To | Smashing Magazine
http://www.smashingmagazine.com/2009/05/15/optimizing-conversion-rates-its-all-about-usability/

In eCommerce usability improvements usually have a huge impact on conversion reates. However, usability doesn’t only mean better visual guide or better site hierarchy. It also means a better communication with potential customers using a professional, trustworthy design, delivering the right information at the right time and communicating with users instead of throwing ad-slogans at them.