Just lately, I came across this [nice list of articles-> http://www.rashmisinha.com/useroi.html] published on the ROI of usability by Rashmi Sinha. Here are some excerpts…

“At any instant, millions of people around the world are trying to use or do something that is difficult or confusing. They may be trying to find a product, trying to figure out how a product works, trying to get service for a product, or trying to replace it. Eventually and inevitably, they will begin to lose time and patience. And, no matter what particular answer they are looking for, the question they pose will be the same: “Why would anyone make something this confusing?…the advantages of creating usable products far outweigh the costs. The rule of thumb: every dollar invested in ease of use returns $10 to $100.” from [IBM's Cost Justifying Ease of Use.->http://www-3.ibm.com/ibm/easy/eou_ext.nsf/Publish/23]

“After Dell Computer applied basic usability principles to its e-commerce Web site in the autumn of 1999, its Web sales skyrocketed. Online purchases rose from $1 million per day in September, 1998, to $34 million per day in March, 2000.” [BusinessWeek - Usability is Next to Profitability->http://www.businessweek.com/technology/content/dec2002/tc2002124_2181.htm]