I'm a big believer in designing for common mistakes. If you know a user is likely to make a common mistake, and there's little you can do to prevent it, I believe the best way to handle it is to anticipate what the user meant to do and do it.

Case in point: In the beginning, nearly all corporate URLs were www.something.com. Almost nobody put their site up at something.com. Then a few companies decided to drop the www for branding reasons. One of the best examples was CNN. Around 1996 they branded themselves as CNN.com, and not only moved their website to cnn.com, but disabled www.cnn.com entirely. Of course, within a month they realized the error of their ways and mapped both domain names to the same machine. In fact, now if you go to 'cnn.com' you're automatically redirected to www.cnn.com.

Companies are very concerned with losing viewers due to the viewer's mistake. For example, it's common practice for companies to buy up the .net and .org versions of their domain such as cnn.net and cnn.org. They want to make sure you get to where you want to go, even if you mess up. This even extends into the academic world (www.ucla.com).

The interesting thing is, while companies will go through a great deal of expendature to obtain domain names similar to their own, (www.yahooo.com), they don't seem to care about the more common mistakes of putting too many or too few w's in front of the URL.

While stats don't exist because almost nobody logs their own primary DNS server, lookups happen all the time for ww.yahoo.com or wwww.ebay.com, and are refused for reasons not immediately obvious to the user.

Site architects should realize the frequency of these mistakes and account for them. It costs no more than a few lines of code in a DNS domain file to map w.cnet.com, ww.cnet.com, wwww.cnet.com or even qqq.cnet.com and eee.cnet.com to map to www.cnet.com. It doesn't harm functionality at all, especially if the web server performs a redirect to the proper connonical name, so even though they type in ww.cnet.com they arrive at www.cnet.com, and it smooths the user experience. It's surprising that designers will mandate that no page take longer than 4 seconds to load, but don't have a problem with erroneous DNS lookups that can take 45 seconds before timing out, leaving the user with a blank screen.

To take it one step further, a DNS server can be configured so that any unrecognized address can be dynamically mapped to the web server (and similarly can be MXed to the primary mail server) so that mail to me@whoziwhatsis.yahoo.com goes to me@yahoo.com whether whoziwhatsis exists or not.

The underlying principle here is that every action a person performs has a base case which occurs if the act is not performed in an expected or acceptable fashion. When walking, the base case is falling down, as you have to keep walking correctly to stay up. In flying, it's hitting the ground. The idea here is to make the base case as pleasant as possible, and whenever possible turning the base case away from a failure case, unlike the examples above.

In Part 2: An example of how to handle failure cases on the other half of the URL or: "The user should never see a 404."