Interesting first piece on business rules over at the Reg Developer. There's some good introductory facts in it - you can check out my FAQ for some more. If like one of the commenters you are not convinced,check out this case study on Egg to see how a real company has empowered its business users to manage some of their own rules to great effect.
One small correction to the article - JSR-94 is a standard, not a rules engine. There is no built-in rules engine in Java which is one of the reason Sun uses Blaze Advisor.
I would also note that some of the rules engines listed support one platform (Java or .NET), some support both but with separate repositories/toolsets and one (Blaze Advisor) supports Java, .NET and COBOL deployment from the same repository, syntax and environment.