Custom Error PagesWebservers can typically be configured to display a customised error page, including a more natural description, the parent site's branding or sometimes a search form. The protocol level phrase, which is hidden from the user, is rarely customized. Internet Explorer (before Internet Explorer 7), however, will not display custom pages unless they are larger than 512 bytes, opting instead to display a "friendly" error page. Google Chrome includes similar functionality, where the 404 is replaced with alternative suggestions generated by Google algorithms, if the page is under 512 bytes in size. Another problem is that if the page does not provide a favicon, and a separate custom 404 page exists, extra traffic and longer loading times will be generated.
Let's take a look at some custom (and funny) 404 Errors (oh yes, there are plentiful out there but just a few examples here):
Source of info : http://en.wikipedia.org