Over at dev.live.com they have announced the release of the Web Page Error Toolkit which “allows you to display custom error messages with search results that generated from relevant keywords.” From the Live Search dev blog:
For large web sites with extensive amounts of content, 2 to 10 percent of traffic is looking for pages that either don’t exist or have been moved. Most web servers return a generic 404 error page or a sitemap when a user’s desired page cannot be found. These unhelpful pages often result in a dead end for users.
With Microsoft’s Web Page Error Toolkit, you can create dynamic 404 pages that contain customized error messages along with search results seeded with relevant keywords to help your users move past the missing page and find the information they need.
The Toolkit is a customizable ASP.net application that replaces the default error page on your IIS server. The Toolkit enables you to use Live Search (or any search engine) to return results for the specified domain and locale, control the number of results returned on your page, choose whether to offer spelling corrections, and customize your error message.
You also have the option of choosing from several keyword extraction strategies that are included with the install, or providing your own implementation.
And a quick example of what happens from the dev.live post:
Typical 404 Error Page
Dynamic 404 Error Page
You can download the Toolkit from Microsoft Downloads