If you're going to be forking off processes to do work for you, I think it's a bad idea to hide the implicit state by using EventMachine to try to manage the pipe I/O and the process state. The reason for that is, sidecar processes screw up, backlog, crash, and eventually start consuming resources you want to track. You end up reinventing the same wheel the Github people did with Resque. Better to reify all those processes from the start with a real queue.

I only make this pedantic comment because EventMachine makes it really easy to start down the path of "just event the process management and I/O", and it seems like you're almost always better off not doing that.