“Research shows that improving the usability of software systems — including information-technology (IT); e-commerce; ‘shrink-wrapped’ and other commercial software — can be highly cost-effective… The rule of thumb in many usability-aware organizations is that the cost-benefit ratio for usability is $1:$10-$100, that is, for every dollar spent implementing usability techniques, the organization will realize a benefit between $10 and $100.”
Link:
http://www.compuware.com/intelligence/articles/usability.htm
