By Charles Miller
BBC Money Programme
Google's ad system earned the company $1.5bn during the July to September quarter of 2005, almost double what it made a year earlier.
And ad income is the power behind Google's stock, whose apparently unstoppable rise makes the financial community's initial scepticism now look humiliatingly wrong.
At the last count, Google was worth around $140bn, almost five times its value at flotation, and comfortably more than the likes of Coca-Cola and Time Warner.
Google's canny founders are also all too aware that Silicon Valley has seen many high tech companies, from Netscape to Pets.com, which in their heyday appeared to be unbeatable, but are now all but forgotten.
