Yes and no. While the syntax of the language is becoming more stable, there are still some pretty big changes coming. Mainly to the core libraries that the Dart team publishes.
Mixins are still in the works (a way to do interfaces... sorta...). As well, interacting with data flows will be changing to use a stream based model. This means if you are doing any server-side Dart and you are reading a file or a socket, you will probably need to make changes to that code with M3 releases.
But ya, the language is definitely getting farther along. One of the more popular books about the language just his the printing presses this week as well [1].
I'm most excited about M2 as it brings SecureSockets (so I can do HTTPS connections) on the server. There are lots of other goodies in M2 (like smaller javascript from dart2js). I also like that they are publishing performance data for 2 tests, showing that the VM is already faster than V8.
