James Robertson's post Smalltalk Tidbits, Industry Rants: Green Screens - Better? is a wonderful reminder of how important information about user and system requirements is only learned by observing the work.
This kind of socio-technical system analysis and design flows from work in Participatory Design started in Scandanavia by the late Kristen Nygaard and others world-wide. This kind of work continues; the eighth biennial conference is coming up.
As system designers and developers we need to keep asking ourselves What is work that our potential users are doing? As engineers we need get out and find out what people are doing and trying to do.