Field Studies: The Best Tool to Discover User Needs
http://www.uie.com/articles/field_studies/

Spool, Jared M.
User Interface Engineering

Abstract:

The most valuable asset of a successful design team is the information they have about their users. When teams have the right information, the job of designing a powerful, intuitive, easy-to-use interface becomes tremendously easier. When they don't, every little design decision becomes a struggle. While techniques, such as focus groups, usability tests, and surveys, can lead to valuable insights, the most powerful tool in the toolbox is the 'field study'. Field studies get the team immersed in the environment of their users and allow them to observe critical details for which there is no other way of discovering.