I would say that always depends on the boards of referees. Generally the success rates are quite high and can easily reach over 50%. That obviously depends on the regions and the boards of referees. It should also be said that people appeal much less than they used to. In other words, when people appeal it's because they generally have quite a good case. That's what explains the success rates before the boards of referees.
On March 3rd, 2011. See this statement in context.