In the advancing ubiquitous computing, relationship between human users and computer systems has been rapidly evolving and getting more complicated. Through various types of users' devices, such as notebooks, smartphones, watches and wearables, and also those that embedded inside our surrounding environment, we let the computer systems “sense” information about ourselves and the physical space, and let the systems “inform” (and provide) various types of value-added and services. In this talk, I present some of our latest work on understanding human activities and even some internal status (such as mood) through various types of sensing technologies spanning from device sensors, mobile sensors, and participatory sensing. Furthermore, I will also focus on the problem of “interruption overload” that occurs when human users' are overwhelmed by an increasing amount of proactive information provisions from the computer systems, and present the latest research on “human attention management”, a research challenge actively researched by the Ubicomp community in the recent years.