What's ESOMM got to do with UX?
A lot. Here's a digital version of a index card that I created a while back after reading this article on ESOMM.
What is ESOMM? It's the Enterprise Service Orientation Maturity Model. I won't rehash the article but if you don't have some ESOMM and you've got web services, life is going to suck for you when it comes to things like service visioning, and migration. Take a look at the following matrix from the article above. Actually, here's the link to "Enabling the Service-Oriented Enterprise" if you don't want to scroll up. This matrix covers all the elements needed for an enterprise. Are your services Usable, Repeatable, Supportable and Extensible? Do you have Implementation, Consumption and Administration strategies?
If you overlaid the index card on top of the graphic (see below), you'll notice that you can use web services, however when you start implementing things on an enterprise level. Things are going to get confusing and painful quick. ("Wait, what version of web service X is customer Y using currently and when do they migrate to web service X version 2.0 with the breaking changes?") Confusing and painful experiences like that are going to ruin the UX (User Experience) for not only the consumers of those services, but also for the enterprise. And remember UX is not just UI, it's architecture.
Sean