  We investigate Bitcoin network monitoring the dynamics of blocks and
transactions. We unveil that 43\% of the transactions are still not included in
the Blockchain after 1h from the first time they were seen in the network and
20\% of the transactions are still not included in the Blockchain after 30
days, revealing therefore great inefficiency in the Bitcoin system. However, we
observe that most of these `forgotten' transactions have low values and in
terms of transferred value the system is less inefficient with 93\% of the
transactions value being included into the Blockchain within 3h. The fact that
a sizeable fraction of transactions is not processed timely casts serious
doubts on the usability of the Bitcoin Blockchain for reliable time-stamping
purposes and calls for a debate about the right systems of incentives which a
peer-to-peer unintermediated system should introduce to promote efficient
transaction recording.
