I came across an Oracle whitepaper with the same title as the post, Doing a quick summary of some of the sections:

Primary SOA value patterns identified are:
- SOA-based Integration
- Modern, Composite Application Development
- Modernizing Mainframe and Legacy Applications

Across the three core SOA value patterns, customers realized order of magnitude business impact - most achieved results in the range of 100-500% improvement.

Customer Stories:

* Customer1 - Changed the game of integration by reducing the response time for integration change requests from two months to five days, delivered without extra budget by nonexpert, internal IT staff.

* Customer 2 - Reduced time to market of a major IT project from two years to six months while improving business users' satisfaction with the application through iterative validation and refinement. In fact, the most enlightened adopters of SOA leverage BPM best practices such as top-down process mapping, iterative/agile development, and layered-services architectures to fight the "business/IT alignment gap" and derive maximum value from SOA. S

* Customer 3 - Fought one of the burning issues of large IT organizations: how to reduce the enormous costs (often 70-80% of the IT budget) and resource needs (30 people to diagnose an issue in tightly coupled COBOL code) of maintaining legacy mainframe systems. After refactoring a COBOL application with SOA principles and technology, bug-fixing cycles were reduced from three to four months with 30 people to three to four weeks with five to eight people.

Five environments that were found to be accelerators for SOA business value and hence "SOA Sweet Spots":
- Constant Industry Change
- Industry Consolidation
- Customizations from Common Base
- Multi-Channel Applications
- B2B Services Network

Source: 1

Prashanth Rai