Way before 1.0 existed (and using an early version of Polymer called WebUI) we built a first version of our app, e.g. http://woven.co/miamitech, which is a fairly complex client and server side application. (The slowness is due to our poor pgsql data design.) I'm now building a more focused version with the latest SDK and Polymer, the beginnings of which are at http://mycommunity.org. For me it's simple: Google is arguably the greatest champion of the open web and probably does more to advance modern web development than most anyone else. V8 was a game changer, and enabled Node. The same folks behind V8 are building, in essence, a better Node. Modern web development with JavaScript is exciting, and there are so many great libraries and resources out there, but there is also much to be desired such as more structure, a saner language and a strong suite of core libraries that play well together. In my experience, Dart is what they say it is: a more structured approach to modern web app development.

Notch (creator of Minecraft) uses it for some smaller WebGL games: http://blog.tojicode.com/2013/12/notch-webgl-dart-and-rampin... and on HN https://news.ycombinator.com/item?id=6841557

Here are people who do: https://www.dartlang.org/community/who-uses-dart.html

I evaluated it. Didn't work in Firefox 31 Beta. Reported the bug. Was fixed in Dart around the time when Firefox 32 RC got released.

Please remember to recompile all your apps you deployed with Dart < 1.6. There are still some Firefox users out there. (Majority in Germany uses Firefox.)