Reading this recent article on Ford's design process for the Fiesta reminded me of the importance of "personas" in human-centered design.
A persona is basically a character that you create to capture certain characteristics and needs of the group of people that you are designing for. The idea is that designers can then better understand and relate to their users - making design decisions less abstract.
In the case of the article above, Ford created "Antonella - an attractive 28-year old woman who lives in Rome. Her life is focused on friends and fun, clubbing and parties." Antonella's love for her cellphone (a characteristic based on market research) led Ford to design a dashboard interface inspired by that of a mobile phone. The hope is then that controlling the features of the car is more intuitive for its users.
I was introduced to the concept of persona's in Dan Gilbert's Designing Learning Spaces class, and here is a great article on personas by Don Norman.