(illustration: ExhibitorOnline via Church of the Customer Blog)

Some people make usability a priority because they think it's important to make the product as good as possible (intrinsic motivation), others are motivated because of what a lack of usability might cost them in terms of product returns, help-desk calls, or degradation of brand image. An argument that is often heard is that poor usability will damage your brand image because it will result in poor word of mouth and that good usability will result in more satisfied customers and thus good word of mouth. Seth Godin gives a number of reasons why word of mouth might not happen, among which:

It might not feel cutting edge enough for your crowd. So, it's not the thing that's embarrassing, it's the fact they you just found out about it. Don't bring up your brand new Tivo with your friends from MIT. They'll sneer at you.