I'm developing with Dart full-time since about 1 1/2 years and I'm just glad that I don't have to use JS anymore.
JS has still more libs ready to use but the quantity and quality of the packages available for Dart are raising fast.
I enjoy that I can use the same language client- and server-side and share a lot of code. Upcoming features will make Dart even more appealing (Appengine support, DartVM in Chrome, async/await, ...) The Dart team is always busy improving the ecosystem :-)
I recently heard someone (Gilad?) say that it's still not "a done deal", but they're confident it will be agreed. Can't come soon enough for me; will make convincing others that Dart is here to stay much easier.