“To the end users, the user interface is the system.” This slogan has been widely used in human-computer interaction field to stress the importance of user interface design. In the Internet and electronic commerce area, the website is not only the system, but it also projects an image of the organization in cyberspace. The design of websites is central to businesses as they create the first impression of organizations to visitors. For a virtual organization, the website is also the only medium that visitors rely on to form their impression of the organization. In this paper, we look at theories and frameworks from cognitive psychology, particularly the Informational and Computational Equivalence theory, and investigate their implications on website designs. A weaker version of the theory, Weak Informational and Weak Computational Equivalence, is also proposed.