SEO Chat has a good article on making your 404 error pages work for you to create increased traffic. Using these methods you can not only retain visitors to your site that have strayed out of your working pages but can also direct them into the areas of your site that you’d like them to head to.
‘Why do you need a 404 custom page? Well, what happens when someone requests a page on your site that does not exist? Have you ever noticed that some sites give you a very nice looking page when you mistype a URL, instead of that nasty 404 File Not Found? It is easy to create a 404 custom page in IIS and Apache.’
This is a technique I’m keen to explore in the new year – let us know in comment below how and if you’ve used these sorts of techniques.