The Need for Web Design Standards

Unfortunately, much of the Web is like an anthill built by ants on LSD: many sites don't fit into the big picture, and are too difficult to use because they deviate from expected norms. Users expect 77% of the simpler Web design elements to behave in a certain way. Unfortunately, confusion reigns for many higher-level design issues.

Nielsen, Jakob. Alertbox (2004). Design>Web Design>User Interface>Standards