We present the first real-world dataset and quantitative evaluation of visual attention of mobile device users in-situ, i.e. while they use their devices during everyday routine. Understanding user attention is a core research challenge in mobile HCI but previous approaches relied on usage logs or self-reports that are only proxies and consequently do not reflect attention completely nor accurately. Our evaluations are based on iContact, a new 32-participant dataset containing around 472 hours of video snippets recorded over more than two weeks in real life using the front-facing camera as well as associated usage logs, interaction events, and sensor data. Using a method for automatic eye contact detection, we are first to quantify the highly dynamic nature of everyday visual attention allocation across users, mobile applications, and usage contexts. We discuss key insights from our analyses that highlight the potential and inform the design of future mobile attentive user interfaces.