Grady Booch has a blog entry on SOA. Nothing revelutionary, but the following is some really good advice when trying to think SOA:
I’ve seen some folks suggest creating an SOA from the bottom up: look at a silo, identify the potential services, and publish them, then weave a system together from them. This is in essence technology first. In my experience, this is a recipe for disaster and/or serious over-engineering.