We call this "Smart404" - eg:
Search.XtraMSN listed this link as a result at their search engine: http://www.nzfootwear.org.nz/Marlboro%20Shoes%20company%20profile.htm
This link does not exist after the NZ Footwear Industry Association moved their site to host with us.. - But click the link and see how we're handling this. We've added a 'SmartURL' entry to forward this missing page to the relevant section within the site. - It's a Smart404 handler.
(This link was available from here: http://search.xtramsn.co.nz/results.aspx?srch=105&FORM=AS5&q=marlboro+shoes+Industry+Association) - and we know this because we track the instances of people requesting pages which don't exist.
Reasons for tracking page requests which don't exist:
A direct example of the Smart404 handler is here: http://www.webdes.co.nz/Smart%20handler (The page linked to here does not exist..)
Our 'Smart 404' handler also matches requests on your website to any page titles, as an example if you had a page on your site called 'Contact Us' and someone typed in the url '/contact us' we'd simply load this content directly out for them making the ID numbered web pages more friendly for you to give to your visitors.
This also helps with Search Engine listings, it makes the named pages available for better searching and indexing.