I'm working on a message passing style RPC using Couch replication and state machine documents, it encourages idempotent responses in the server's async processes, which is similar to functional operation.
My own RPC system enforces continuation passing style exclusively to unify the calling and return-value semantics. With this functional pattern in place it was pretty straight forward to transparently wrap arbitrarily many closures arbitrarily deeply in callback argument lists and method requests (which are the same thing under continuation passing style).