As @jaberg mentioned, `generate_dot` has some implications. Additionally, GraphViz recommends that people use the file extension `.gv` because `dot` isn't their only tool (there's also `neato`, `twopi`, etc.). So I would say rename to `generate_gv` or `generate_graphviz` or maybe `model2graphviz` or `nengo_to_graphviz`... just throwing those out there!

I also think that this is a more generally nice thing to have, and so I'd recommend it be placed in `helpers.py`. It's not just for builders!

And, I wonder if there's a use case for passing it a model instead of separate objs and connections lists. Maybe have two functions: `model_to_gv` and `objects_to_gv` (where `model_to_gv` is just a one-liner calling `objects_to_gv`).