Jakob Nielsen's Top 10 Web Design Mistakes

Jakob Nielsen started his "Top 10" list in 1996 and last updated it in 2007.  He says he hasn't updated the list since 2007 because Web designers are still making the same basic mistakes.

1. Bad Search — Stick to a simple box, which is what users look for, and make sure your search engine can handle typos and other common variants of search terms.
2. PDFs for online reading — They break users' flow and are hard to navigate. Save them for printing and convert your information to Web pages.
3. Not changing the color of links users have already visited — Users need to know where they've been.
4. Text that's hard to scan — Add subheds and bulleted lists, highlight keywords, and keep your paragraphs short and devoid of fluff.
5. Fixed font sizes — Let users resize them if needed.
6. Page titles that have low visibility in search engines — Start with the company name or other most relevant few words.
7. Any design that looks like an ad — Users will ignore it.
8. Lack of design consistency — Users should know what to expect.
9. Opening new browser windows — Users get confused (see 8).
10.  Not providing basic, up-to-date information, like your price lists or your menu — That's what users want most.      

For more information, visit his site.