Good luck competing with a company that controls the underlying frameworks you're building your development environment for. There will never be a truly viable alternative to Flash Builder from Adobe as long as they control the runtime. Depending on third party IDEs for a proprietary API is shaky ground to build a business on.
I have not, but my concern would be becoming dependent on a third party Flash development tool for my workflow, and then being left behind as Adobe adds new features to the runtime unsupported by the IDE I'm using, or worse, that they find a way to break content created with the competing IDE. I don't think such a possibility would be all that unexpected, given Adobe's competitive nature and refusal to cede control of the runtime.
