David Chappell has just posted a good primer explaining exactly what Service Component Architecture (SCA) is and why we should care about it.
In the paper, David explores the properties of components, SCA's Java Component Model, composites, policies, and implementing SCA.
David acknowledges in in his conclusion that vendors have had their own agendas with SCA:
"...when someone says 'SCA,' he might mean any or all of the things these specs define. Similarly, different vendors are almost certain to emphasize different aspects of SCA. One vendor might support SCA’s assembly aspects and its new programming model for Java components, for example, but not the C++ version of this model. Another might support only SCA’s assembly aspects, completely ignoring the new Java and C++ programming models. And since these specifications explicitly allow vendor extensions, look for each vendor to provide some customization in its SCA products."
Still, SCA offers an alternative to older approaches such as EJB and JAX-WS, and has a lot of vendor support, David says. "Anyone who’s interested in the future of application development should also be interested in SCA."
On an additional note, while vendors have their own agendas with SCA, David points out he received no compensation to write and publish the paper -- he did it for the love of the technology.