Watch this episode of Dartisans and learn more about using Dart with Web Components. Even though Web Components aren't yet baked into the platform, you can use Dart to build Web Components today and compile them down into code that works in modern browsers.
You can follow along with the open-source dart-web-components work on Github.
With Dart, you can build structured web apps. With Web Components, you can build encapsulated, declarative components. Two great ideas that go together!