BI Review has a great article on using business rules to automate insurance underwriting - Decision Management Evolution. There are some key points in this about how to go about this in terms of process and planning ideas, highly recommended as an outline for how to do rules right.
Mike ends saying:
At ACG, we have been able to reap the rewards of a decision management application that would be beneficial to all companies. The power to dynamically manage the business rules to drive customer strategy, maintain decision consistency and empower business agility have all contributed to the improvements to our operations and yielded great gains on our overall business performance.
I also wrote more about this customer here if you want more.