Nielsen Norman GroupEvidence-Based User Experience Research, Training, and Consulting
The ten most egregious offenses against users. Web design disasters and HTML horrors are legion, though many usability atrocities are less common than they used to be.
Structure and navigation must support each other and integrate with search and across subsites. Complexity, inconsistency, hidden options, and clumsy UI mechanics prevent users from finding what they need.
Bad content, bad links, bad navigation, bad category pages... which is worst for business? In these examples, bad content takes the prize for costing the company the most money.
Application usability is enhanced when users know how to operate the UI and it guides them through the workflow. Violating common guidelines prevents both.
Weblogs are often too internally focused and ignore key usability issues, making it hard for new readers to understand the site and trust the author.