According to the company, the feature shaves off 2 to 5 seconds from user searches since it brings up results nearly as fast as it does for its auto-suggest feature. In fact, it will automatically do a search for the top auto-suggestion before a user has even selected it.
Google estimates that if all its users switch over to the instant interface, it will amount to a savings of 11 hours of searching per second.
Despite the instant results, users are still able to use Google in the traditional sense, by typing in a query and hitting the enter key or search button. Users can also opt out of using it on their search pages, or from the Google Instant search itself.
To give it a spin, you can follow this link. Worth noting is that you'll need to be on Chrome, Firefox, Safari or Internet Explorer 8 for the new service to work. It is also limited by location to users in the U.S., most of Europe, and Russia.
You can also check out my colleague Stephen Shankland's first impressions here: "Google Instant: Better but not revolutionized search."