Search results that are personalized in this manner carry a special icon identifying them as such. No one else but the signed-in user sees them.

It will be interesting to see what reception this Gmail search feature receives when and if it's made widely available. Privacy has been a concern on and off for Gmail since it was launched back in 2004. At the time, many criticized Google's decision to run text ads in the service based on the content of messages.

Years later, Gmail was at the center of one of the company's worst privacy fiascos, when the now-closed Buzz social network by default and without permission generated a public list of initial contacts for users based on their Gmail contacts.

For now, the new search feature is in limited testing. Those interested can apply to participate in the field trial by going to this page: https://www.google.com/experimental/gmailfieldtrial.

In Wednesday's blog post, Singhal also said that Google soon plans to extend its voice search feature, now available in Android, to iPhones and iPads running iOS 4.2 and above.