This may be bitcoin 101 that I just missed but it would be great if someone could flush out some justification to what Friedcst said about transaction fees becoming a bigger part of the reward for mining a block. Why is it that this will happen? 15 btc per block seems like a lot in fees. What sort of fee per transaction would that equate to?
We're doing a lot of extrapolation here since the number of BTC issued per block isn't set to halve again until ~ 2017. At today's transaction amounts - aka 50K transactions per day or about 350 transactions per block this would be about .04 BTC per transaction. However, we have to presume that the number of BTC transactions will significantly increase as BTC gains more popularity. Anyone want to take a guess about how many transactions per block in 2-3 years?