More on error pages in the wild and the customization thereof (of lack thereof).
But first, a quick review. A Mr. Enduser on a Web browser requests a file. For some reason, an HTTP response is generated from the server other than 200 OK -- let's say the requested file cannot be found by the Web server, and a 404 response is generated. On IIS, the default settings will map the response to serve Microsoft's default 404 error page, which looks like this. Nice, you served an error page, but the jolt for Mr. Enduser in being taken from a nice, well designed page on your site to a scary error page like the example above means that 95% of users will abandon your site on the error. Not good, so this is where customized error pages come into play...
An error page is an excuse for why you could not serve the user, or at least it should be. Some sites, like RushLimbaugh.com, don't give the user any reason for the error:
RushLimbaugh.com 404 error page
No help there (not surprised given the source). Rush doesn't make his living off of the site, so let's take a look at the error page from AOL.com, a company that has made a real online bidness for itself:
AOL.com 404 error page
AOL gives us a bit more of an excuse in defining the error, but not a bunch of help with where to go (and where are the images, a link, that famous "You Gots Mail" AOL brand and that little running man guy? -- bummer). Exploring other error pages, we find that some folks simply won't take the blame when an error occurs on their own site:
Mytwinn.com 404 error page
For shame, for shame, mytwinn.com. It is your error -- help the user to get to some good content, don't blame the sites giving you inbound traffic, even if it is misdirected! Apple.com does not tell us that is a 404 error, per say (Apple is famous for obscuring errors beneath a great user experience), but they do give us a wealth of options on their 404 page (and it coordinates with the rest of their site design AND has some deals as well):
Apple.com 404 error page
So the moral of this tale? Custom error messages are good. Give people options. Make an excuse, but make it a believable one. Smart custom error design will keep Mr. Enduser and other browsers on the path that you want them on: getting deeper into your site or Web app.