Unfortunately, we're not willing to release details before the fact because of the risk that people will game the system. Here is what I can tell you:

The plan is to give away 50 billion of the 100 billion ripples. The rate at which they're given away will be determined by how quickly we can actually give them away and how quickly we believe we can scale the network and maintain its reliability.

Now, speaking officially for OpenCoin: We are committed to being transparent after the fact. We are committed to giving away 50 billion XRP. For each give away, such as the current Bitcoin Forum giveaway, we will publicly disclose at least how many people participated in the giveaway and how many XRP were given away.