When you're able to take Dart and reliably, run it on both the server and the web client then it may be interesting. Right now I don't see a good use case for it right now.

For one, debugging client-side code is going to be annoying especially if you end up running into a bug due to the Dart to JavaScript translation. You're going to have to know Dart and JavaScript well in order to debug effectively.

The other side of the coin, server-side, as far as I can tell isn't really ready for prime time (at least that's what the Dart language website says unless I'm misunderstanding them).

Neat idea but I don't see the practicality yet. In all honestly I don't understand the trend to move away from JavaScript especially when all it does is translate into JavaScript. That seems like an extra layer of abstraction that isn't very useful to me especially in debugging.