What does Personal Interaction have to do with effective software development? Lots! As Jerry Weinberg says, "It's always a people problem." As the [http://www.agilemanifesto.org/ Agile Manifesto] states, "Individuals and interactions over processes and tools."
Effective teamwork starts with effective interaction between individuals.
Techniques to improve interaction
For further learning
[http://www.ayeconference.com/ AYE Conference] -- Amplifying Your Effectiveness
[http://www.estherderby.com/workshops/secrets.htm Secrets of Agile Teamwork] by Esther Derby and Diana Larsen.