Our key technical insight was that people type slowly, but read quickly, typically taking 300 milliseconds between keystrokes, but only 30 milliseconds (a tenth of the time!) to glance at another part of the page. This means that you can scan a results page while you type.
The most obvious change is that you get to the right content much faster than before because you don’t have to finish typing your full search term, or even press “search.” Another shift is that seeing results as you type helps you formulate a better search term by providing instant feedback. You can now adapt your search on the fly until the results match exactly what you want. In time, we may wonder how search ever worked in any other way.
Marissa Mayer: “It’s not search ‘as you type,’ but ‘search before you type.'” “We can predict what you are likely to type and give you those results in real time.” (via RWW.)
Google claims that Instant will save many users 2-5 seconds per search, and, if used globally, will save humanity a collective 3.5 billion seconds per day. Personally, I find it a little distracting, though you can turn it off by visiting your Google Preferences page.
One purpose for which it does seem useful, however, is mobile search: Google says they will have this out later this fall.
Google will be rolling Instant out over the course of the next few days; if it’s not already enabled for you on Google.com, you can hit this link to try it out. Thoughts?