Why do we use what we use? Why do we love some applications and hate others?
Human: Experiences which fulfill us are the ones we engage with at both emotional AND rational levels. The definition of fulfillment is different for all of us—that's what makes us human.
Technical: Technology should never drive—it should enable. But don't you ever underestimate it. That shiny new iPhone you are waiting for won't do you any good if it can't make a simple phone call.
Aesthetic: We're attracted to beauty. Beauty is in the eye of the beholder—as is ugly. But we know both the moment we see it.