In this blog entry - From ESB to ESP: action-oriented SOA - Joe McKendrick - discusses the SOA Maturity Model being promoted by some SOA vendors. The first time this 5 level model mentions rules is in level 5
Level 5: The SOA information systems becomes the "enterprise nervous system" and takes action automatically according to events occurring at the business level according to rules optimizing business goals.
So does this mean that business rules is a technology suitable only for the last level of maturity? I don't believe so.
When getting started at level 1 business rules can be a huge boon. Not only are decision services an obvious first service - the desire to decide consistently across channels and across systems is often a key driver for SOA - but they also represent a great way to take part of an existing system and expose it as a service. I wrote about that approach here.
When an organization reaches level 3 and starts to try and manage responsiveness then the use of business rules will start to show a strong return. Business rules are ideal for adding business agility to a process and will allow SOA-enabled processes to show additional responsiveness.
Lastly, of course, rules-driven orchestration is essential to level 5 in this maturity model. I have written on orchestration and business rules before.
Have fun, and don't wait for level 5 before making business rules part of your SOA approach.