I spent a few minutes and made a custom 404 page for this site. Try hitting any non-existent page like http://myvogonpoetry.com/thispageisnthere and you can see it. Hit refresh to see a different version of it. If you are running Apache it’s really easy to create a custom 404 page – you pretty much just have to create a page and put it somewhere on your site then at the root of your site you put a .htaccess file that has this in it:

ErrorDocument 404 /path/to/errorpage

You can even do some fancy stuff with like PHP like show the user what URL they were trying to access. Here are some examples of error pages I did on my other sites (I really like the one I did for thebrokenkoystick.com):
http://thebrokenjoystick.com/thispageisnthere
http://pipasoft.com/thispageisnthere