I've been experimenting with Dart, trying to get my feet wet, and I just recently published my first Dart library!
In ActionScript world I use as3 signals everywhere and moving to Dart I felt lost without it, so I decided to make a custom implementation of it for Dart.
I am aware that Dart doesn't use Events, and instead it uses a stream/subscription model, which is actually quite similar to Signals, and is very fast performance wise, but there were a couple things that seemed a little more complicated to me.
That is, if you wanted to remove your handler, as far as I know you have to retain an instance to the subscription object, then use that to remove the handler. I'm not a dart expert by any means, but I can imagine this could add clutter to a typical use case.