Roger Session's latest ObjectWatch newsletter relates planning a SOA implementation to thinking about how pilots win dogfights.  The moral of the story - iterative development is a winning idea:

"Boyd [an Air Force Colonel who thought about winning dog fights] teaches us that we win by iterating faster than our enemy, not by building a more expensive plane than our enemy. We will do better by implementing and deploying a small piece of the SOA, getting it right, showing its value, learning from the result, and then iterating on to the next piece."

The benefits of iterative development is an idea that keeps coming back to me from multiple angles.  It was the key idea I took away from a recent 3-day training course on the Microsoft Solutions Framework.  It's one of the key principles from Lean Development and from the XP's idea of iterations.