I recently found the article 'Is Web 2.0 The Global SOA?' which creates a linkage between SOA (Service Oriented Architecture) and Web 2.0. The article readily admits that "both Web 2.0 and SOA are already slippery, nebulous concepts", but that nevertheless there are "unmistakable patterns within each that actually are very tightly related, though wrapped in slightly different cloth".
The article does a good job in identifying the common aspects and the differences. Coming from a business perspective, both concepts deal with best practices for building business processes into vast supply chains. In contrast to Web 2.0, SOA has the concept of orchestration - (although mash-ups in Web 2.0 are coming close).
On the other hand, "Web 2.0 embraces people, collaboration, architectures of participation, social mechanisms, folksonomies, real-time feedback, etc. All things that SOA, in its grey, dull, corporate clothes, does not, at least not explicitly."
The article concludes with "Yes, so Web 2.0 is a global SOA, done right for the whole world. It's big, it's everywhere, and it's here today."
A similar article notices a dysfunctional gap between SOA and Web 2.0. This gap can be bridged by making the semantics of it's parts more explicicit, allowing the different parts to interoperate (and also making both concepts less nebulous and slippery). There are currently several efforts to add semantics for SOA and Web 2.0. Efforts like WSMO (Web Services Modeling Ontology) are aiming at adding semantics to SOA, whereas efforts like SIOC (Semantically-Interlinked Online Communities) are adding semantics to Web 2.0.
It will be interesting to watch how the different efforts converge - my expectation is that Semantic Web 2.0 gets more service oriented, whereas the semantic SOA need to get more consumer oriented and lightweight in order to facilitate such a convergence.
It is an interesting space to participate...