Business logic, embedded in services fabric implemented through SOA, is not a monolithic determinstic entity. Rather sevaral externalities like regulation, changing business dynamics, partners have to be addressed in order to minimize continous changes to the core services.
Recent outages experienced by service providers had a cascading impact on downstream mashed-up website raising issues of reliability & availability. Use of external services leads to rise in risks levels that might not be within the consumers (of web services) control. How do you build redundancy in such cases i.e. multiple providers of equivalent services??
There might even be cases where for building in differentiation in QoS parameters to different consumers. This article published by SETLabs researchers gives a good overview of the challenges ahead, also proposes a practical architecture to address QoS issues in Web Services management.