principles of usability:

some things to think about

Typically, users score lower than designers on spatial reasoning and visualization tests.
Most web designers are young, and so have perfect vision. Tiny text doesn't bother them as much as it bothers people on the other side of 40.
Designers also tend to own expensive, high-quality monitors that are easier on the eyes.
While creating a website, designers don't actually read the information on the pages. So they aren't aware of how their design may actually affect using the site.
[kids] are typically more immediate than adults and tend to act on what's visible.
"Lower-literacy users exhibit very different reading behaviors than higher-literacy users: they plow text rather than scan it, and they miss page elements due to a narrower field of view."
This information was summarized from:
http://www.useit.com/alertbox/20050711.html
http://www.useit.com/alertbox/20020819.html
http://www.useit.com/alertbox/20050314.html
In the United States alone, 8 to 12 million people have severely impaired vision.
- NYT News Service, 10 April 2002

The Word on website usability is at: http://www.useit.com/