There's a very informative article in InfoWorld about how Con-Way, the trucking company used SOA to migrate away from their legacy applications piecemeal. The effort required making the architecture explicit first, with the right level of granularity, and then building interfaces. Then various parts can be changed as needed and reintegrated to create new apps. The article says:

Although the Con-Way effort began eight years ago, the basic architecture has remained stable and has allowed the company to change its technologies while maintaining the underlying business logic and adding new business logic as the market demands.

From Lessons from an SOA pioneer | InfoWorld | Analysis | 2006-01-06 | By Galen Gruman
Referenced Fri Jan 20 2006 06:40:38 GMT-0700 (MST)

This reminds me of IBM's experience in creating the System 360 architecture. The architecture was stable over several decades. If designed right, architectures should be very stable over periods of many years.