I recently read The Tipping Point by Malcolm Gladwell and must say it has had a profound impact on how I see information design and the world in general. It is the concept that little things make a big difference or "tip" an idea, concept, or product from mediocre to widespread adoption. The book is filled with many in-depth case studies that reinforce the concept and help you become more familiar with how our minds work, how our culture works, and what links it together.
One interesting thing the book mentions is how the TV show Sesame Street became successful by doing iterative usability type testing on kids. They used the testing results to drive tweaks to the show that eventually led to the success. They used testing to figure out what the show needed in order to "tip".