It turned out to not only work - but blow my expectations out of the water. The group not only had a very fruitful live discussion but people were hacking away on the Etherpad. The interesting thing which happened, was that people started to have conversations on the Etherpad itself - people agreed, disagreed, argued and sharpened their arguments. We ended up with about 10 pages full of extremely valuable comments, thoughts and ideas. The Etherpad software itself handled the onslaught of more than 50 people hacking on the same document at the same time with grace and created a fascinating visual artifact as participants could see how thoughts were developed in real time (which we also projected on the main screen). I highly recommend giving Etherpad as a backchannel a try for your next public talk. You can download the Open Source software here.