The issue is not a gap between what librarians think our current customers need and what they think they need. In fact, we are pretty good about understanding our current customer's basic needs (yep, they need everything online so they can print it off!).
Instead, the gap is between what our customers think they need and what they are actually doing! This question is what ethnography tries to answer.
I agree that we are good at understanding our patrons' basic needs (and being able to access everything online so they can print it is highly important at my library too). It is the third sentence that I think we need to think much more about. Ultimately, there is often a definite gap between what users say they need and what their actions imply they may need. In the reference class that I took last this past semester, there were several readings about how reference librarians need to carefully listen to the user and often times negotiate with the user to better understand what the user is asking for. Librarians need to pay attention to body language, mannerisms, etc. in order to hear what may not be explicitly stated. These points were heavily stressed in the readings and especially in the textbook.
I'm wondering if this is why we often make unconscious assumptions about what users want. It seems that we rely heavily upon our own interpretation of events when it comes to the users and have been taught to do so. If it is necessary to make interpretations when helping users with reference questions then it seems to me that we must also make interpretations about what users say they need in terms of library services and systems. How do we do this without imposing our own biases, knowledge-base or without unconsciously deciding what we think is best? How do we truly get a clear picture of our users and what they need?
I think it is obvious that usability testing and studies is one of the main ways that we can figure some of these things out. Users don't always articulate their needs accurately - I think this is because they are often asked to tell us there needs in an artificial situation (a survey). Actually watching them try and find information, answer questions and use services can tell us much more about their habits and about what roadblocks they encounter along the way. I'm actually interested in reading more about the ethnography approach. This sounds like a very interesting way to learn more about users and how to make meet their needs more efficiently.