AJAX is an exciting new technology that allows us to create an almost seamless interface in the browser which provides the user with an application like experience rather than the jarring page renditions of most web experiences. The cost of this facility is a barrage of exchanges back and forth to the web server that puts a tremendous load on the web server. Further, the technology offers the promise of a push experience but can only do this via the use of polling. There are constant rumors about how AJAX might evolve to allow needed updating without polling, but until that develops, it will remain a small niche technique for select kinds of interface updating.
SOA's are supposed to be the next evolution of distributed systems. Recently we have begun to see commentary that suggests that like so many other paradigms, SOA will be DOA. I think the final evaluation is still out. In the late 90's, HP's espeak presented a significant effort in this direction that dies with the many problems HP faced in the market place. Regrettably, this rather elegant, and complete solution has disappeared. The most recent manifestation of SOA as Web Services has made back a lot of ground, but the implementations tend to be weak on the provision of malleable registries that can be used to discover services located on repositories. Until registries begin to appear, the testing and development of webservices or SOAs will languish.