Tina pointed to NY Magazine's short article on the architect/designers, Massimo and Lella Vignelli. There's a great quote in there that speaks about how the Vignellis arrive at solutions to design problems, and is certainly appropriate to the work we do while working on user experiences for the web.
It’s a matter of discipline, and it starts by looking at the problem and collecting all the available information about it. If you understand the problem, you have the solution. It’s really more about logic than imagination.