The California DMV recently replaced the portion of a legacy system that dealt with license fee calculation with a business rules implementation. This was the one part of the old legacy system that had variable business rules - it required changes whenever the legislature changed the law. Now the California Legislature, like most, can't resist tinkering with the license fee calculations. This meant that the system must constantly adapt to new rules about licensing, even though most of what it does stays the same. By using business rules technology for this one component the DMV was able to dramatically reduce how long it took to get changes into production and eliminate much of the cost of these changes. The use of business rules to manage this kind of highly volatile component is one of the classic first uses in an organization.
If you want to try these rules out yourself, you can. Check out the Vehicle Registration Fee Calculator or read about the awards this system won - Intelligent Enterprise RealWare Award and Application Development Trends Innovator Award.