A recent CBDi commentary says "SOA is ... not the silver bullet that many are suggesting; it's plain hard work." The article is obviously intended to make people think they need to pay for CBDi research reports before entering the scary world of service oriented architectures, but once you get past that, there's some pretty good information in there regarding what an SOA is and what that definition means to architectural choices about coupling and components. If you're an SOA expert, you can skip it. If you're trying to figure this out and build a mental model of what an SOA is, I recommend it.