While the smallest fraction of bitcoins currently implemented is the Satoshi (10-8 BTC or 10 nBTC (nano-bitcoins)), due to transaction fees there seems to be a minimum amount of BTC to be spent that is larger than one Satoshi. What is currently the smallest amount of BTC one can spend at comparably little to no fees. i.e. what is currently the smallest sensible unit of microtransactions?
I personally think that the most smallest and sensible transaction is at least 0.0001
HOWEVER NOTE: If you want a confirmation in 10 or 20 minutes, you will need to post a minimum transfer fee of 0.0001
So technically If you want to transfer 0.0001 to a account you will need at least 0.0002
If you want to transfer a bigger amount, the transaction fee will not need to be changed e.g. If you want to transfer X amount to a account you will need at least X amount + 0.0001
I have tried to transfer 0.00005593 with no transaction fee, and there is still no confirmations: https://blockchain.info/tx/15ee5484920eed92457643a1709629d8ff579b15fc805b0060a9cf0efdcbb8ed
Transfer More faster = Pay a Higher transfer fee
Just to note: transfer fee same as Miners Fee same as transaction fee