I've been following Dart on and off since it's announcement. I'm still a little skeptical of the language, but I'm a fan of what they want to do. Here are their basic goals:
- Create a class based (OOP) language for doing browser heavy apps (like GMail).
- Make the language easy for Java/C++/C# developers to learn.
- Only work with "the modern web". meaning IE9 and higher.
There is a lot more to it than this, but it's sort of a beginning. The language still hasn't hit 1.0, so no one is seriously using it (as the language itself was seeing large changes up until recently). Google has not talked about anyone outside of the Dart team itself that is using Dart within Google (they are doing it, it's just not being talked about yet).
Since 1.0 is expected this summer, you probably won't see many people using it until that milestone is hit. Once 1.0 is hit, people will be more willing to create real products with it, so you can expect to see more about Dart after that. As well, once the DartVM makes its way into Chrome (which will happen sometime after 1.0), you'll probably see a lot of press about the first Google App that is written in Dart.
It's still early in Dart's life. The only people really seriously using it are people that like learning new languages. Companies and most developers won't touch an in-progress programming language out of fear that syntax and behavior changes will screw them up.