How to implement inter-process communication in Go?

I'd suggest looking at 0mq. It's a messaging library designed to be be fast and easy whether you use it over the network, for local IPC, or even inter-thread communication. It handles a lot of the tricky bits of IPC, like making senders back off sending requests if the receiver is getting overloaded, message framing, and reconnecting after failure. And it has bindings for LOTS of languages, including Go, which makes it useful for wiring together systems written in different languages.

Go has a built-in RPC system (http://golang.org/pkg/rpc/) for easy communication between Go processes.

Another option is to send gob-encoded data (http://blog.golang.org/2011/03/gobs-of-data.html) via network connection.

You shouldn't dismiss local networking without benchmarking. For example Chrome uses named pipes for IPC and they transfer a lot of data (e.g. rendered bitmaps) between processes:

Our main inter-process communication primitive is the named pipe. On Linux & OS X, we use a socketpair()

-- http://www.chromium.org/developers/design-documents/inter-process-communication

If named pipes are good enough for that, they are probably good enough for your use case. Plus, if you write things well, you could start using named pipes (because it's easy) and then switch to shared memory if you find performance of named pipes not good enough (shared memory is not easy regardless of the language).