I would like to hear from you what you think about potential use of mocking frameworks when testing distributed systems that involve different AppDomains, threads, processes and even machines. Then we no longer talk about unit testing - these are clearly integration tests, but they may have similar needs in regards to object mocking.
Imagine you need to test a multi-tier system integrated with database and external components (Web services etc.) You need to examine how the system responds to various error states. Of course you can spend some time on writing stubs, but it would be so much easier just to configure imaginary mock server that would simulate behavior of certain objects.
Doing this in environment with multiple processes and machines is not something supported by available mocking frameworks. On the other hand it does not look so complicated to extend the framework to implement persistance and session-based mocking. I wonder if such features have been discussed or even considered.