If you begin considering emerging self-metrics that measure, for example, your routes through cities, fitness level, social status, and state of mind (think Foursquare, Nike+, Facebook, and Twitter), you realize that there is a compelling universe of information waiting to be pinned to the back of each image. Once you start thinking of a photograph in those holistic terms, the data quality of stand-alone cameras, no matter how vast their bounty of pixels, seems strangely impoverished. They no longer capture the whole picture.
Taking and sharing photos on a Smartphone makes the practice of photography more fun (network effect) and contextual (e.g. #fromwhereirun).