I use Dart in production, it has its advatages like:
1.- It is better than JavaScript, is like using C# with a litle mix of Java.
2.- It comes with its own libraries, no more underscore.js or other patch libraries that JS needs, it is already in the toolkit.
3.- It comes with the Dart Editor, where you can debug your code easily, for scalable projects I find this to be invaluable.
4.- It will run in all your browsers, because it will export your code to JavaScript, but not only export it, it will optimize it and will run really fast.
5.- The pub library, go to pub.dartlang.org and you will find lots of packages that you can install and use, like a bootjack, a bootstrap port in Dart.
There are prolly many more, but these are the ones that come to my head right now.
But it also has its own problems like:
1.- No Dart support for Chrome yet and we don't know if there will ever be at this point.
2.- The generated JavaScript will be huge, and I mean huge, mine is like 460k per file and I'm not using polymer, when I used polymer the generated JavaScript was over one megabyte, just insane in the cloud.
3.- Get use to regressions, with every point update I've have issues, I upgraded from 1.4 to 1.5 two days ago, now my code is broken It runs, but it will for example run futures twice, So I went back to 1.4 for now, I had some other issues with UTF when migrating from 1.3 to 1.4 so, get use to.
4.- They are slow fixing bugs, looks like polymer and speed are their priorities, but when you need something trivial that other languajes have had for years and you report a bug it will get ignored, I've waited for 18 months and my open bugs are not fixed yet.
I would say that Dart is nice and you should give it a chance.