I've been thinking about bitcoins.

If there is some way clearing houses can prove they own a certain quantity of bitcoins, then, the bitcoins don't need to be physically transferred. This has some advantages. Firstly, the bitcoins can be secured off the grid. Secondly, the transfers between clearing houses are simply bookkeeping entries, meaning there is less bitcoins that need to be actually exchanged. In the event of fraud, there is some traceability and reversibility, since clearing houses can implement rules similar to what banks already do. For instance, monies deposited cannot be withdrawn straight away, until it is clear that there are no other claims on the money.