Creating custom 404 error pages

Does your site have a custom 404 error page? What does it include? How often do your site visitors encounter this page? Please share your tips for customizing 404 error pages.

This topic was derived from Builder.com’s Design and Usability Tacticse-newsletter. If you aren’t already subscribed to the Design and Usability Tactics e-newsletter, visit our e-newsletter subcenter to sign up for this TechMail today:
http://builder.com.com/techmails.jhtml?repID=u001