One of the common things in any application is getting access to current user or other session-like information from the domain objects. It can be usually done with static members (the horrible thing!), injecting a service (so there should a place to get the service from, like dependency injection framework).
I've done just using a bit mixed solution with ECO. So there's a service registered in the ECO space (lifetime is the same as EcoSpace' one) and there's an OCL operation that accesses the modeled global data object.
Just putting a not on how to get access to the transient global data object. It doesn't use the service but just relies on ECO internals in full.