DontPissPeopleOff

It's difficult at times to make a site that meets all your users needs, but don't set out to deliberatly annoy your potential customers, each one could become your biggest fan. Such as:

• People with Accessibility issues
• Older Users
• Mac Users
• Non-broadband users
• People with older computers
• People who have turned off JavaScript
• People who share a computer
• People with a small monitor
• People with a huge monitor

See:
AccessibilityIssues
http://del.icio.us/theotherblog/Accessibility∞
Article on designing for the elderly∞