Jakob Nielsen has updated his Top ten mistakes in web design document for 2007 an its well worth a read. Nielsen is quite often seen as too "hard line" and his ideas are often seen as too restrictive to work in practice but I think this list of ideas and suggestions is something that every web developer would do well to read and understand.

Points that I particularly agree with are:

• 2. PDF files for online reading
• 3. Not Changing the Color of Visited Links
• 5. Fixed Font Size
• 6. Page Titles With Low Search Engine Visibility
• 9. Opening New Browser Windows

All of these are bugbears of mine and are so common in many high profile websites that "ought to know better".
Check it out at http://www.useit.com/alertbox/9605.html