Loren Goodman, CTO of my company, presented an excellent topic on Microsoft TechEd conference Getting to the Handshake: Leveraging Business Rule Technology through Architecture, Design and Practice which can viewed and downloaded at http://www.msteched.com/2010/NorthAmerica/ARC301. It highlights the growing interest in this area in the community since people are into rules more and more as they redesigning existing solutions and engineering new ones and the understanding of the flexibility in the first place is a requirement which is one of the core one. You can find more on the current state of the Rule Engines on my company's site at http://www.inrule.com