Right now I skip from writing heavy JavaScript in the UI (AngularJS) to writing Python on the server. It's a context switch, how I iterate over collections, parse strings, etc. is totally different. I'm not in love with Node.JS, but love the idea of a single language/code constructs throughout the stack. Especially in a small-team startup environment. Maybe someone can come out with a synchronous server-side JS engine? :)

Just realized that it's also a context switch when I go from Python to Mongo, especially when I'm working in the Mongo shell.