I realize transactions can come in a wide variety of sizes so my back-of-the-envelope calculations need to be taken with a big grain of salt;

https://blockchain.info/charts/n-transactions-per-block shows around 3-Mar-2014 a peak of 618 transactions in a block (as averaged over 24 hours) & https://blockchain.info/block-index/477556 is a 396KB block with 710 transactions in it.  1BTC/710txn ~= 0.0014BTC/txn or about $0.53 at the current exchange rate; so much for micro-transactions.  Also, 396KB/710txn ~= 558B/txn, so, 1MB/558B/txn ~= 1792txn/MB.  Even, 1BTC/1792txn*$377.79/BTC ~= $0.21/txn.  I think maybe 0.1BTC/block would be nice.  If exchange rate climbs to $2000/BTC and if the block size were still at 1MB then 0.1BTC/1792txn*$2000/BTC ~= $0.11/txn but if the block size were at 2MB then the per transaction fee drops to $0.055 or so.  As legit transaction rates climb presumably so does the exchange rate.  At what point does BTC decouple from fiat?