It's a tough call, but I certainly do think there should be some form of punishment because a false accusation could be treated as an action of harmful or malicious intent, therefore punishable by law. Perhaps such a punishment should only be carried out if a unanimous decision is reached about the suspect's innocence, and if there is any misconception or split vote, then neither party should receive punishment. Despite this meaning some rapists may walk free, I think that with the increasing frequency of false accusations, this is the fairest way it can be done since rape is so difficult to prove.