I was talking with Microsoftian Scott Woodgate yesterday and he let me know of a lacuna in my toolbox: BizTalk 2004 has a forward-chaining RETE-based rules engine. I've never heard of anyone using this technology (BizTalk's implementation, I mean -- I've used (and written) rules engines before). Dang. Not enough hours in the day to check this stuff out, but I've got to make time...