Steve Krug says that usability is about building clarity into web sites: making sure that users can understand what it is they’re looking at — and how to use it — without undue effort. Is it clear to people? Do they “get it”?

But there’s another important component to web usability: doing the right thing — being considerate of the user. Besides “Is my site clear?” you also need to be asking, “Does my site behave like a mensch?”

Usability as Common Courtesy