I'll admit I have not tried this because everytime I get outhunting I forget what I am suppose to do. So I end up having to fire an arrow into the ground. Luckily I never hit anything to damage the arrow, but my brother did ruin one of his doing it this way.
Anyway, if you are one of these people who need a visual aid, you can watch the video on how to uncock your crossbow here (2:55 mark):
http://www.summerfield.ca/excalibur/ropeaid_256k.wmv
I think I'll have to try it out, looks pretty simple and alot easier.