I evaluated Node, intrigued by the idea of event-driven, non-blocking client and server side code written in one language, but I found it to be a wild ecosystem with dozens of frameworks and not enough support and guidance for them.

I found Dart with its promise to bring some structure and sanity to that approach, including building a language from the ground up to do away with JS's quirks, and it has delivered. I built http://woven.co with Dart and Polymer.

The biggest pain is when you'd like to use a JS lib that isn't wrapped for Dart yet. They're hard at work to make it much easier to interoperate. They're a kick ass team, great docs, first class support in WebStorm, and its future seems bright. There are issues with Polymer like SEO that are inherent in any SPA really, but there are experiments with React-like Virtual DOM diffing and others too.

On the server, the dart:io is powerful and Shelf looks like an awesome set of abstractions for http servers and more that I hope to play with soon.

Dart is treated with heavy skepticism I think often unduly, but judge it for yourself and I think you might be pleasantly surprised.