that’s an interesting take.
You need to see the full-res render of the key before you send it to flash so I put a white background under my clip for keying purposes, render it and watch it, and then blow away the background when I’m finished and leave it UNrendered.
I guess the default black background is misleading then. I know you can change it in FCP, but perhaps it should be checkerboarded like photoshop. how annoying would that be? yikes.
…or perhaps in future versions there should be an on/off layer selector in the export window.