Spy has an interesting article on the limits of usability as a primary design component:

Usability--and the cautious thinking it embodies--has come to dominate thinking about the design process. As Robert Brunner, a partner at in the San Francisco office of the celebrated design firm Pentagram, will argue at the HITS conference in Chicago this week: "it really doesn't matter if something is usable. What matters is that it is in fact, useful. And even better if it is desirable" [vii]. This possibility of making someone's experience of a product both successful and satisfying is more likely to be achieved in more mature areas of design, such as newspapers, where complex patterns of communication have been established with which elements that produce an overall 'quality of experience' can be incorporated. If usability becomes the focus too early in the development of a product it is likely that a more ingenious and ambitious way of solving the problem will be missed, and a less useful and desirable solution will be polished to perfection.

One of the areas where users are almost always not our best critics is when disruptive ideas emerge:

Too much user focus may be a barrier to innovation. Research with users is likely to tell us that they desire an improvement on something they already know and understand – faster calculators rather than spreadsheets. Ask them if they would use a proposed innovation and they will say No – and then adopt it when they have seen its utility demonstrated in the real world.