I used haxe for over a year creating dozens of end-user apps when I was working at chumby industries because our base runtime on those devices was FlashLite 3 with ActionScript 2.0 and haxe is a significantly better language than AS2 while still targeting the same Flash runtime.
IMO it is definitely a language worth checking out, particularly since it should be trivial to learn if you already know the language for whatever runtime it is you're targeting. It looks and feels very much like ActionScript/JavaScript, but with far less warts than either.
The macro system it has is awesome and allows for lots of compile-time code generation scenarios that can result in massive runtime optimizations if used well.
http://www.haxenme.org/showcase/ http://www.haxenme.org/showcase/page-2
Of those in the community developing flash only games, I have encountered a strong tendency to move away from AS3 towards haxe simply because you get the same API with a better language, faster compiler and faster code.
The weak point of Haxe is in library bindings. As a relatively young language, It doesn't have bindings to the breadth of things that C++ or Python has.
The guys behind NME have made the workflow almost completely painless with a simple command-line tool that will download and install everything required to do development on a variety of platforms. See details for setup here. http://www.haxenme.org/developers/get-started
The disadvantage of NME is that it closely mirrors the Flash API. That's great if you are aiming for cross platform flash/other, but if you want to drop flash from your supported targets there are probably better API styles (which I believe is where Nicolas is heading with h2d)
I have written Games using NME, The Flash API directly and the HTML5 canvas directly. I'd like to have something that provided a Cross-platform glES interface across iOS, Android and WebGL/Javascript but currently no such system exists for haxe.
One of them that I know personally is a professional Flash developer who used haXe exclusively for some times, because it had a better standard library than Flash (AS2 at this time) and generated lighter and faster SWF files. I remember him telling me that he made a somewhat huge (several hundred euros) donation to the project and that it still cost him less than buying the Macromedia Flash software. Since AS3 he's back to Flash thought.
Some others I know through their work: Motion Twin [1] for instance, who are the creators of a lot of very successful Flash games.