actually Gilly - I unclip at the top of the stroke. The thing I have to remember is to make sure my front tire is turned in the direction of the "unclipped" foot, especially if on a hill. That way if you lose your balance, you'll "fall" on the unclipped foot.
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, champagne in one hand, strawberries in the other, body thoroughly used up, totally worn out and screaming: "Yeah Baby! What a Ride!"