The key to success with any new system is simplicity and ease of use. Apple, the most valuable company in the world, is a prime example of this, their products are well designed and simple to use.
Lack of simplicity may be part of the reason for a growing pushback against the new i-Park car parking machine system being installed in the CBD, particularly as the old "drop in coins until you've paid for enough time" method was simpler than the new method.
In my opinion, change was desperately needed to the car parking system. The old system offered a lack of consistent payment method across the CBD, plus the old meters are an eyesore and take up valuable space.
The new system improves this, but it does add additional steps - find a parking machine, enter your number plate, select how long you wish to park for and pay.
However, not all machines accept coins, and if you find yourself at a machine that only accepts debit/credit cards you will be pinged a 50 cent surcharge for the pleasure of using your plastic.