If Google Instant is everything that Google hopes it will be, the entire industry of search engine optimisers and marketers has some work to do.

The new search feature, launched at a slickly staged event at San Francisco’s Museum of Modern Art (Google is finally learning some of the Apple magic), predicts a user’s intent and returns results as a query is being typed. With each additional keystroke, Google says it can make a fresh calculation of the most likely search query and show instant results.

In theory, as Googlers on hand like Marissa Mayer and Sergey Brin were quick to point out, this should make no difference to the eventual results or the adverts that users click on. The ranking algorithms remain the same. But in practice, Instant could have far-reaching effects.

It all depends on how users adapt to the new service. Here are a couple of possibilities:

Winner takes all. Instant could greatly amplify the most common search results, which will be displayed repeatedly in front of users. When that is a commercial entity, the impact could be significant. Type any query beginning with the letters “Am” into the search box, for instance, and Amazon is likely to be the first instantly displayed result.

When I put that to Mr Brin earlier, he suggested the impact was likely to be minimal, since users would only look down and click on a result that matched the intent of their original search. But he conceded that these  are effects that will need to be studied. Certainly, the value in terms of brand recognition from all those inadvertent searches could be huge.

Another winner-takes-all effect could follow if users change their search behaviour. Instead of entering a full search term, then looking down a list of search results to find the one that is most relevant, they might instead keep adding text to the search box until the right answer (or one that is good enough) magically appears in the top position. Studies have already found that the top few results win the lion’s share of clicks: in future, winning top spot may be all that matters.

Impact on click-through rates. The click-through rate that advertisers use to determine how often search engine users click on their messages is calculated by dividing the number of impressions of the ad that are served up divided by the number of clicks. But with Google Instant, what is an impression?

Google says the average search query is 20 characters long, so in theory it could show 20 different sets of search results (with accompanying ads) each time a user types in a request.

To adjust for this, Google says it will only record an impression once a set of results - and ads - has been displayed on the screen for three seconds. When I asked Ms Mayer about this, she said the three seconds was based on a “cognitive pause” - the time it takes a user to stop and absorb a set of results.

But will that be enough time to take in the adverts? Ms Mayer said that eyeball tests to assess where users look on a search results page show they are drawn heavily to the left-hand track, which shows options for how to refine a search further. Will they look as often at the adverts on the right?

The three-second rule (which will also be used to determine what Google counts in future as a “search”) could be adjusted as needed. But the company admits that it does not know yet how users will interract with search results - and ads - as the search experience turns from a static query/results formula into a more fluid process.

If the new feature works as advertised, users should find their way more quickly to relevant results. And in the search world, more successful searches should bring more clicks on ads. But practitioners of SEO and SEM may need to relearn the art of getting the right result and the right ad in front of users in a way that they will notice.

by Richard Waters