I always got stuck when debugging within the IDE using trace was no longer an option, think about Externalinterface or a simple fullscreen event. When stuff like this doesn’t work, you are fubared.
But now I have this: http://www.demonsters.nl/producten/debugger
It’s free and works like a charm. It’s even possible to run public methods run-time in the live app trace.
It really is God’s gift to AS-programmers