As people we are emotional beings. With the exception of maybe habit, Everything we do affects us in an emotional way. If you just sit back and "people watch", so-to-speak you'll notice these emotions in subtle yet powerful ways. Software and Web interactions are no different. The most exciting part of this emotional existence we have as people is that it's insatiable. As people we NEED to emotionally experience our world as much as we need to breathe. In fact, I believe that emotion and experience are so tightly coupled in human beings that they cannot be separated.
Commercially speaking, a company who is able to adequately embody and productize an emotional experience can not only penetrate commoditized markets, dominate them despite late-entry, but can also create new ones which are difficult to predict with traditional business plans. Internally, these companies can increase productivity, morale and thereby strategic advantage.
The risk? Emotional experience is difficult to predict and is most evident in observation. Emotional development or, "Design Driven Development" as we call it here at RRIPL, is based upon observation of existing use cases. It also requires an iterative approach since the tipping-points between positive & negative experiences are not immediately obvious.
I think Frank Spillers, from Experience Dynamics, does a fantastic job of introducing a starting framework for building a positive UI experience.
