I'd also wondered about the transition to transaction fees. It's not clear that it'll be an easy transition. So I took about 2000 of the most recent blocks from the block chain and I'm not seeing any real change in transaction fees over the last 2000 blocks. The average is 0.075 BTC in fees per block. 50% block come below 0.03 BTC, 80% below 0.1 and 95% below 0.3. I don't have transaction figures yet or any stats for more than 2000 blocks. That'll have to be another night, I've already spent too much time on bitcoin tonight.