Check this 404 Not-Found page of Yahoo !!
http://www.yahoo.com/abcdefghijklmnop.html
This page will get redirected to homepage of Yahoo !! In 10 seconds using the below meta tag !!
< meta http-equiv="refresh" content="10;url=http://www.yahoo.com/?l=1211971226" >
NOTE:
l=1211961175 is a auto generated key !! I suppose Yahoo is not using it right now but it will use it in future so as to redirect the visitor to the related available pages on yahoo !!
Benefit:
When a user coming from search engine or via some website will find that the page he/she is looking for does not exists !! He will probably leave the website redirecting him to the Home Page or to a page with related content matching to the keyword he/she was looking for !!
If you have any query about applying this let me know !!
That number is a UNIX Timestamp. Probably to keep the page constantly “renewed” in your cache.