that's why i said it rules out micropayments
well, not by the conventional definitions of micropayments (under $20)
some people take micropayments to mean payments of a couple of cents, say to read single news articles. it's not useful for that. the transaction cost is too high. but for small payments it does beat visa!
The bitcoin micropayment ( / nanopayment limit if you like that as a better term mouse) is 0.01btc - at current bitcoin prices that translates to US$0.169 - bitcoins transferred under this value at present will attract a compulsory transfer penalty. It protects the bitcoin blockchain from transfer spam.
This limit however will be adjusted dynamically depending on future bitcoin prices and blockchain volume.
At a certain service provider holding your bitcoin in credit, you would be able to transfer any minute amount of bitcoin without any penalty if it is internally to the service provider, see mybitcoin.com for example where transfers of any minute amount is always free.