As I mentioned in a previous blog, I see Net-centricity as a "collaboration" umbrella concept where the mindset revolves around leveraging the power of the collective whether it is people or systems. I view SOA and Web 2.0 as the two sides to the net-centricity coin.
I remember the words used by one of my favorite high school teachers when trying to express to us students that although physics and chemistry are mostly treated as different disciplines they are actually very closely related. He used this definition that I found very useful, "Physics is the study of mass and energy with an emphasis on energy while chemistry is the study of mass and energy with an emphasis on mass."
Following this model I offer that SOA is the construction of systems and human interactions with an emphasis on systems while Web 2.0 is the construction of systems and human interactions with an emphasis on humans.
No definition is perfect but I think this explanation captures that they both center on interactions between entities each with its own bent but also involving a good amount of overlap. Mash-ups are a great example of the overlap between SOA and Web 2.0.
