Google 404 Error Pages Become Intelligent and More Useful
If you happen to type a web address on Google that doesn’t exist (e.g., google.com/yahoo, google.com/adsence), you are no longer shown the default 404 Error Page that says "The requested URL was not found on this server."
Since errors like 404 are like greek to most people, Google is taking a more user friendly approach and they now try to guess the page you are looking for.
For instance, if you type google.com/email, it suggests you the Gmail website instead of displaying the regular "Page Not Found" error.
Similarly, a typo like google.com/blog will throw in suggestions pointing to the Google Blog Search Engine. A very neat approach.

Update: You will still see the same old 404 page on Google if your erroneous URL has a file extension (like google.com/labnol.html or google.com/secret.php)
Related: AdSense Publishers may show ads on 404 Error Pages according to the recent AdSense Policy changes.

Doesn’t do that for us. Probably you are using the new version of google toolbar ???
You seems to find these things before everybody else does (including top blogs). Great job.
However, In my testing I found the same old 404 error page. I tried the same url as yours. Probably, Google is still trying it.
I cant see any changes yet. :(
Did you try any of the following Google addresses:
1. http://www.google.com/email
2. http://www.google.com/blog
3. http://www.google.com/sex - this should suggest the official Googleplex domain and the Google CSE page (Custom Search Engine)
Does not work for me either - tried all your 3 examples and I still get the old:
Not Found
The requested URL /email was not found on this server.
I think you are getting confused with a google search feature — if a specific page you are looking for is not found, then google search tries to be helpful and some of the suggestions may infact be what you are looking for.
And in browsers that default to searching for a page that does not show up and if google is the configured default search engine and perhaps if google toolbar is installed, then the 404 error results in a google search for the page you were looking for.
Sanjay - this is not connected with Google Search. This is about pages and directories hosted on the Google.com domain.
Have uploaded few more screenshots on Flickr.
this seems to be another move of Google to provide better services to users . Does the same work with Google’s Service-domains , like : Orkut and analytics ??
None of the 3 URL’s work the way you said it would.
It is the same old
Google Error
Not Found
The requested URL /email was not found on this server.
same here Amit
none of the URL’s are working for me too…??
why is it so that only your system is showing the changes..??
I got it working now. I think it is taking time to reflect the change in all the locations.
luck for you find this… but its not work for me.
Hi Readers,
This only works with new Google Toolaber Beta 5.
this feture is available from last 6-7 months.
cheers
Matt Cutts issued a “clarification” a month or so ago regarding this toolbar function.But this is entirely different since I dont have the toolbar version installed