I've been spending a lot of time recently looking at how a service oriented approach helps around older applications in particular how it helps to move them from being static systems into more agile and responsive ones. During this I've done quite a bit of research into how much people spend just on "keeping the lights on" as opposed to actually moving forwards.
Its about 80% of the IT spend out there. Which means that for SOA to actually matter, namely making the 80/20 rule apply to SOA then its actually going to be not about new technologies, web services and the like, its going to be about how we reduce that 80% and start making existing systems pay for themselves.
The goal of SOA is often touted as being the regeneration of these estates, but most of the time I'm just seeing people proposing new IT projects that aim to put "lipstick on the pig" of legacy applications. This isn't solving the problem its just trying to hide it, and is liable to be as successful at hiding it as EAI was when it promised to do the same thing in the late 90s early 00s.
This is why I argue that SOA has to be about changing the way you think about your IT organisation and the IT estate. It has to impact not just new technology builds, but more critically it must impact the old technology. This means that SOA must change the way that application maintenance is done, the way that help desks are set up and the way that change requests are handled. It even means changing the way IT is organised and in particular the current "handover" of applications to the life-support system that most applications move into once they go live.
SOA's buzz and hype is driven in the desire to sell new projects and sell new technology licenses, this misses the opportunity for most companies which is to move their IT organisation away from a project or technology focused approach towards being truly organised and responsive to how the business operates.
People have often said "you can do SOA with CICS/COBOL" and they are right, I'd go further in fact. If your organisation isn't doing SOA in its legacy and old ERP systems then you are just playing with new toys and aren't actually solving the problem that IT has created.