Nobody complains about how measuring cups work. But the OXO measuring cup was designed after careful observation had identified a problem that nobody had really ever noticed before.
It's well worth watching this video for more details about the product development process at OXO: http://goodexperience.com/2010/08/a-product-development.php.
I haven't seen a better demonstration recently of identifying unmet needs through careful observation. The presenter, Alex Lee, plays down the skill and depth of insight required in being able to observe people doing very common and familiar tasks and identifying the breakdowns that occur. It's difficult because as observers, we are so familiar with the activities we are observing that we take the same things for granted that the people we are observing do. Great observers work hard at stepping out of their comfort zone so that they can observe from a completely different perspective, always asking 'Why is it like that?'.
One of the techniques I try to use in these situations is the master-apprentice technique from Contextual Inquiry (http://en.wikipedia.org/wiki/Contextual_inquiry). In it, the observer acts like an apprentice, learning from a master (the person being observed). It helps me drop any biases or preconceived ideas I might have about the activity I am observing since it reminds me that I am learning from the master and that there are many things about the way the master does their work that I don't know anything about.