How does (or perhaps should) change control work for applications your users use which arent owned/hosted by yourselves. Say for example a key application which is a web based app hosted on someone elses infrastructure. When they announce they are due to move to a new release and upgrade their system - how should that tie in with your internal change control systems? As the end of the day your end users could still be affected.
I know one element of change control is user acceptance testing - which again I find hard to see how and when you get the opportunity to do so when the system is external.