Snap! Ayende Rahein has shown how Active Record can be used to implement a rules engine. I'd had some thoughts about backward-chaining and LINQ lately as part of a forthcoming post, it's nice to see some groundwork laid.

BTW, this is via Sam Gentile, whose blog is very high quality and who's looking to increase his subscriber base. Definitely subscribe if you're looking for high-end advice on agile techniques for advanced .NET development.