Standard 404 page
I had a bit of a scare this week. If you accidentally type in www.google.com/masp instead of www.google.com/maps, you get this:

Not really what you’d expect from Google.
What is a 404 error page?
A web server shows an error 404 if it is asked for the url of a page that doesn’t exist. Because the page doesn’t exist anymore, for example. Or because the user made a mistake in typing in the url.
A standard 404 error page looks pretty unattractive and isn’t very useful. The best thing you can do is create your own 404 page. On that page you should put your logo, main navigation, the message that the page the user is looking for doesn’t exist anymore, maybe a few suggestions and a search feature.
Practice what you preach?
What makes Google’s lack of a customised 404 error page so strange is the fact that they give tips about how to make your 404 pages more useful on their blog. An oversight? Or strategy?
A big thank you to Elja Trum of Photofacts.nl for pointing this out.
HTTP requests are expensive so making an HTTP request and getting a useless response (i.e. 404 Not Found) is totally unnecessary and will slow down the user experience without any benefit.
Some sites have helpful 404s “Did you mean X?”, which is great for the user experience but also wastes server resources (like database, etc). Particularly bad is when the link to an external JavaScript is wrong and the result is a 404. First, this download will block parallel downloads. Next the browser may try to parse the 404 response body as if it were JavaScript code, trying to find something usable in it.
Google’s 404 page has been redesigned
Yes it has been redesigned it’s much better now
http://yfrog.com/h3xll8p
In above case it is showing that “/masp” not found. So user can get idea that he has misspelled Maps. Still it is true that error page should be more interactive. Great stuff.