Checkout Rapidminer and Knime for great examples of box'n'arrows applied to machine learning pipelines. I've used Rapidminer a fair bit and they really have a great model including a dynamic number of inputs/outputs from a single box and ability to make boxes that encapsulate pipelines made from other boxes. I was able to do an order of magnitude more experimentation using this visual style than if I had tried to script it in code. I'm a software engineer who loves to program so the fact that I'd pick this tool for that job over programming I think says something.