According to more recent research, people can remember about 3-4 things (for about 20 seconds) and then they disappear from memory unless repeated over and over. In addition, people tend to chunk information into groups that have 3-4 items in them. On top of that, researchers tell us that people can’t effectively choose between more than 3 to 4 items at a time. Source: What Makes Them Click

I’ve been studying up on the Serial Position Effect, which includes the Primacy Effect, and the Recency Effect. Basically stated, items first in a list are put into long-term memory, and so therefore have a competitive edge when it comes to remembrance, and items last in a list are stored in the working memory, which also allows people to remember them more quickly. The list items in the middle are more easily forgotten.

The Relativity Trap, or the Anchoring Effect, is this: people think about prices relatively. This is why recommended retail prices are set high, then discounted, or why there are always some expensive options on restaurant menus, making the regular meals look reasonable in comparison. Source: PsyBlog

According to a study by Jakob Nielsen (and numerous others), people spend more than twice as much time looking at the left side of a web page (69% of viewing time) as they do the right side (30% of viewing time). This is part of why I’ll never make people scroll horizontally.