For clients that are wondering about the effect of Google Instant (GI) on SEO, here is some information.
In summary, we believe Google Instant will make SEO more relevant. Fewer people will see the same results page and therefore localisation and relevant keyword targeting becomes even more important.
Probably the most interesting change is going to be how people search. They will most likely search more (use search variations to find the most appropriate results) and they are likely to construct their search phrases more carefully. This will then boost the importance of long tail search and perhaps reduce the percentage of users clicking through beyond the first page of the search results.
In terms of PPC, Google Instant will effect how page impressions are calculated for click-through rates. An impression will now be calculated when a click-through takes place or if the user pauses for 3 seconds.
Introducing Google Instant
Additional Information on Google Instant
Marrissa Meyer on Google Instant and SEO among other things.