Dartium, Chromium with an integrated Dart VM, has been in development for a while, but now Dartium binaries are available from Google.
Previously the only way to run Dart code in the browser involved compiling it to Javascript, but with Dartium it's now possible to see how Dart code performs on an actual Dart VM in the browser.
Dartium also contains the beginnings of Dev Tools ѕupport, ie. debugging and other features. Seth Ladd has a demo of Dev Tools in Dartium. The debugger support is a work in progress, but breakpoints and similar features work already.
Dartium improves Dart development in Chrome, but the language also has a live outside of the browser. A look through the Online API reference for Dart shows the Dart I/O API for files, sockets, and more. The APIs can be used synchronously as well as asynchronously.
These APIs are already used in Frog, the Dart to Javascript compiler written in Dart, which can run on the Dart VM and use the file APIs to do its work.
The amount of resources for Dart developers has grown in the past months. Chris Strom is busy writing "Dart for Hipsters" and he's posting his notes and experiences with Dart on his blog.
Google's Seth Ladd's blog is also a rich source for information and updates on Dart, both for the language and the SDK tools around it.
The official site also now has Dart Synonym, a page showing the Dart equivalent of Javascript snippets.
The official Dart site has a blog tracking developments. A recent post pointed out a list of projects using Dart, which includes projects like three.dart a port of the popular Javascript 3D library three.js, which makes it easy to build 3D code for both 2D Canvas or WebGL.
For a background on Google Dart, see InfoQ's 'The Essence of Google Dart', and other InfoQ Dart content.