Google's influential search engine has hit a tipping point in technology's shift to smartphones. More search requests are now being made on mobile devices than on personal computers in the U.S. and many other parts of the world. The milestone, announced at a digital advertising conference, serves as another reminder of how dramatically online behavior has changed since 2007. That's when Apple released the first iPhone, leading to a wave of similar devices that have made it easier for people to stay connected to the Internet wherever they go. The upheaval has rocked PC makers and other tech companies such as Microsoft with businesses tied to sales of desktop and laptop computers. Google has been able to adapt better than most companies, partly because its search engine and other services are embedded in the popular Android mobile operating system, but it hasn't been totally unscathed. Google's average ad prices have been d...