I don't think there is any difference between money (dollars, pounds, euros, yen) and an IOU.
It is just an IOU issued by a very trusted institution.
As such it functions as a general unit of value transfer, because it is worth the same to both sides of the transaction.
That is what we all think and how we all act, but there unit used (dollars, pounds, euros, yen) to transfer value change over time so it isn't the same to both sides of the transaction. The value of the unit is manipulated by FRB and the Central Bank.
It is akin to a builder changing the units of measure so he can reduce his building expenses and claim he has done a good by coming in under budget.
* edit
The money meme can only work effectively for all participants in the economy if the unit of measure is fixed, or if it is an actual commodity that is readily exchanged, then the unit of measure must be fixed to the commodity. It should be fraud to create a mechanism that allows banks to increase the unit of measure but not the represented time value commodity. FRB is thus the mechanism behind the business cycle, allowing Malinvestment in economic activities and unfairly distributing the risk.