I read this post from Anne Thomas Manes about SOA and SOI. I have to disagree with the assessment. SOA does not have to be extremely disruptive to be started or to be successful. SOI, don't love another acronym, is a very good way for companies to actually get started down the SOA path without the major disruption.
Standards based integration with Services as the focal point can lead to the reduction of the very legacy systems Anne is talking about. If done correctly the plumbing can make the transition to SOA more fruitful and less impacting to the overall business. The idea you have to rip all the systems out and rewrite everything as a service is kind of far fetched.
One of the key issues with SOA adoption and success in my view is this kind of talk. It's the over engineering discussions that either paralyze an organization into inaction on the SOA front or cause an organization to go on some mass rip and replace tear that ultimately has very negative impacts.
Start simple, don't over engineer, don't go on a shopping spree, don't try to explain SOA to your business. Another massive IT project is probably the last thing your business needs right now.