Once a website's speed has been optimized, proper presentation is the final step. The following brief list is vital to any website: colors, whitespace, content, and navigation. The utilization of color and whitespace is the first step in a visitor's evaluation process. Cluttered pages and/or inappropriate colors will deter users within the first second. After users achieve a basic comfort level, they begin to scan content. This is where content layout can shine. The appearance of titles, sub-titles, headers, and content must be clear. The word "scan" is important. During the evaluation period users do not read, they browse. Websites that are difficult to scan frustrate people. Users that find the content mildly satisfactory may choose to look elsewhere within a website for relevant information. In this scenario, navigation is a website's final opportunity. It must be easy to find, understand, and use. Don't forget that website search fields are another form of navigation.
User acceptance testing is a great way to test the 3 Second Rule. Get a website in front of users and record their interactions. Take notes and ask lots of questions. People are always willing to provide feedback. Keep an older, slower computer handy to test minimum design and connectivity requirements. Don't alienate these individuals.
One of Google's early principles was speed. The founders recognized that connection speed and patience were inversely correlated. A few years ago Google jumped into the browser arena with their "fast and simple" philosophy. Their approach has been very successful. Google continues to show that speed and simplicity matter.