In recent years, Silicon Valley seems to have forgotten about silicon. It’s been about dot-coms, Web advertising, social networking and apps for smartphones. But there are signs here that hardware is becoming the new software. It is an expansion of a trend that began a few years ago with the Flip videophone, a sleeper hit, and has recently accelerated with Nest, the smart thermostat; Lytro, a camera that refocusses a photo after it is taken; and the Pebble smartwatch, a wristwatch that can interact with a smartphone.