Problems with the Australian currency:

The size of the coins is (in ascending order); 5c, $2, 10c, $1, 20c, 50c. The silver coins have value increase with size, but with the gold coins, the $2 is smaller than the $1.

A lot of Parking meters and some vending machines don't take 50c coins because they are so damn big.

The 50c coin doesn't roll and you can't use the notes to make origami.