As a longtime Python guy, mostly back-end (but I knew JS pretty well) -- I did a quick demo site recently in node, and was surprised by how it felt. There was much less context-switching as I went back and forth between the client and server. That sounds obvious but it was kind of a shock.

I always wanted Python on the client (here's looking at you, Jython!) -- js on the server may be the closest thing I'm going to get.