Yes, you want happy customers. How in a usability test can you evaluate if your prototype experience fits together with a happy customer.
Tomorrow at Red Privet we are doing a round of usability testing. More/Better happiness is a valid and useful goal for software/service design. How can happiness be measured in a usability test?
In earlier work with the end-users we were able to map the experience in the image below. In the bottom half of the image you can see the ups and downs of error/problems as the end user would go through the stages of the journey. Then we asked the end user to put a smiley face on the the stage they were most happy at and a frown on the stage they were most sad at. In a similar way, I'll ask "What part of the prototype that you just used was the most satisfying?" OR "What would be the high point and the low point of using the tools that we just went through?"