404 pages report to your users that a page they wanted is gone. But you can use them to tell you about problems and suggest solutions. But to use them, you need to read your error logs. I was working on a CGI today, and to test it I was watching the error log on the server. While I was watching a bunch of errors came through for another site on my server. In an update I had done last month had removed a page that people still access. I went in and added that page back - netting that site an additional 100 pageviews per day. Too bad I didn't see that sooner! By reviewing the error log regularly, you can solve problems your readers might not tell you about.