Hi, I'm an engineer on Montage. We decided to use Dart to help manage the complexity of a large HTML5 application. From this standpoint, Dart has been amazing. We value having a structured language that supports optional typing, libraries and namespaces. So being able to have language features like this has been very productive for web development.

If you do choose Dart for your next web project, you'll probably decide between using Angular.dart or Polymer.dart for building your UI. Polymer is Google's implementation of the emerging Web Components spec. The project is still early, and they're still hammering out the implementation. It seems like things are stabilizing though, but don't be surprised if you face some gnarly bugs or breaking changes. Angular is probably more mature, but I don't follow the project closely enough.

We started working on Montage before the Dart versions of Polymer and Angular. Because of this, we're using WebUI, which is the predecessor to Polymer. We plan on migrating to Polymer soon.

Hopefully this is helpful. I plan on writing up a post that goes into more detail of our experience with Dart.