EDIT: A lot of crashes later - I have designed a fixed bracket which flies quite OK.. or as OK as one may expect on a arDrone - it can be found online at shapeways.com/model/422364/beefy_gopro_hero_bracket_for_the_ardrone___rear_fa.html
Having flown a series of "missions" gaff taping the camera all over the hull of the ar.drone the last two days... I learned closer to the COG is better. This test is as tight as it gets without cutting the hull apart. Camera is under the front with gaff tape just in front of the cross bar entry point - the battery is secured with gaff on the rear of the hull to balance the setup over the position camera. start from grass with the camera in the grass. I added some Zip ties to extend the legs which helped.
The first part show take-off and stabilize - the ardrone stabilized nicely with the load.
Video processed in iStabilize the black frame clearly show how the air-frame moves when encountering turbulence in flight.
Conclusions so far - this can work - straight crane shots, and stable shots with the ardrone moving smoothly in one direction is very promising.
*I did a halfway tear down later, cutting the front half of the hull, and mounting the GoPro case to the hull, stable moves OK, but the drone really is not that keen on weight.
Hmm. I should expand on that. the ar.drone actually fly very nicely with the GoPro in case and all mounted dead-center on top and low, however the drone are not much for moving the arm out much.
Next step - tear the hull apart and rebuild with a gimbal mounted camera.
Update - same ardrone with smoother camera mount - vimeo.com/22518609
BTW - Some very nice things have been done with the arDrone - take a look at some of my favorites
This one is maybe the most effective use I have seen of a ARdrone so far, very nice, but also clearly show the limitations of the ardrone as a arial platform.