I met Roman Kiss in person at the MVP Summit today, and had a great conversation about how to provide an intra-process solution when performance is critical and you don't want to pay for the creation of transport channels unless you absolutely have to.
Roman has done a fantastic job documenting this on CodeProject: http://www.codeproject.com/KB/WCF/NullTransportForWCF.aspx
The idea is that even IPC requires necessary transport channel creation to marshall between processes. The Null Transport, as Roman calls it, provides communication within the same Application Domain. So, it isn't as close to the metal as you can get, it *is* bare metal.
This is a brilliant approach to providing intra-process communication within SOA while providing the same level of flexibility that any WCF client/service gets via binding/transport choices that are, for the most part, post-depoloyment decisions.