Google Instant is Google's new and improved search method which use's Google's vast storehouse of data to anticipate what users are looking for, even when they aren't sure themselves. You could call it mind reading, but new science always looks like magic, and this is a baby step in the direction of the semantic web. I've used it and am pleased with it, for being subtle and unobtrusive, as well as mind-blowing. Technical folks are in awe of what Google has wrought.
On a stockholder level, you could argue that Google Instant is more about increasing margins by reducing costs, specifically Traffic Acquisition Costs, which represent the cost of running the network and software required to make search come to click.
More efficient searches (fewer round trips to the Bigtable in the Sky to get to your click) means less network activity per click. Of course, the increased density (velocity) will result in more clicks per unit time.
Google is tuning the Internet to its bottom line. Nobody else does it better or more relentlessly.