I'm in the early stages of something "real", and I'm finding it very useful. I think if someone is already very familiar with and is mostly happy with JavaScript and its ecosystem, they might not see much of value (or maybe they would). For me, however, I can get small things done in JavaScript but tend to be overwhelmed by the ecosystem, and I'm far more comfortable in Dart. The core libraries are great, and having class-based object-orientation makes me much more comfortable than the prototype stuff in JavaScript.

Blossom.io CEO wrote an amazing blog post about their decision to switch to Dart in production: http://www.ramen.io/post/46936028144/we-are-switching-to-dar...

Northwestern Uni just published a post today describing their good experience of choosing Dart to teach their HCI class:

http://amartya.in/post/48107255194/introducing-dart-to-an-hc...

Yes. I'm in the process of finishing up a touch enabled web app for a client and we're all very pleased with the result. Since Dart is in development and has been changing, I've stuck to a small subset of features, basically easy DOM manipulation with classes. The resulting JavaScript from Dart2js has worked flawlessly across browsers (Chrome/FF/Safari on Win/Mac/iOS.) I believe there will come a time when clients specify Dart because it saves them time, money and maintenance problems.

One of my favorites: http://glyph3d.com "Glyph3D is a font atlas generation tool. It enables game developers / artists to create beautiful font atlas maps using various filter effects."