I'm excited about this as an alternative to the IPython notebook, but with more of an IDE feel. This means the notebook can focus on what it's good at without adding more IDE-like features.
IPython notebook looks great for what it does, ideal for scientists who need one off scripts and be able to show their working, but that and the rise in online IDE's seem like a step backwards for a serious developer. They are great for getting started, but are seriously lacking in other areas.