I have been meaning to find out exactly what the laws are here in the state of South Australia because ignorance isnt an excuse. (guilty as charged)
So I called in to see the police.

Here is a summary of my visit and I found out the laws have changed since my incident.

When questioned about carrying my leatherman:
Response: “you can carry it for any lawful purpose but not near or on a licensed premises especially after 9pm. Also you are not allowed to use it for self defense.” (Licensed meaning serving alcohol)

When questioned about carrying a normal knife:
Response: “why would you want to carry a knife?”
My response “ I want to know what the law is because I carry one when bushwalking or camping etc.”
Response: “you can carry it for any lawful purpose, there is no size or type limit, apart from prohibited weapons. example: if you buy a knife at the camping store and we ask you what you are doing with the knife and you say “I have just bought it and Im going to the car” is ok. But if you are walking down the night club district in Adelaide (State capital city) with the same knife you would be prosecuted for carrying an offensive weapon. If you are going camping, leave it in the car until you get there then carry it.”
He then gave me a leaflet on weapon laws.

Summary: it seems that you can be charged for carrying any knife.

Some things of interest from the leaflet:
There are 3 classifications of weapons: 1. Offensive Weapons 2. Dangerous articles 3. Prohibited Weapons

1. Offensive Weapons
Anything can be an offensive weapon if it is carried or used in a way that is offensive or with intent to harm others.
It is illegal to carry an offensive weapon without a lawful excuse.

2. Dangerous article
It is illegal to manufacture, supply, deal in, possess or use a dangerous article without a lawful excuse.

3. Prohibited Weapon
It is illegal to manufacture, supply, deal in, possess or use a dangerous article unless exempt.

An example given under Offensive weapons is carrying a hammer in a nightclub at 2am.

Examples of Dangerous Articles
blow gun or pipe, slingshot, dart projector or archery dart slinger, capsicum spray, Self protection device (device that emits electric current/energy or sound )

Examples of Prohibited Weapons
Ballistic knife, Catapult, shanghai, slingshot with a brace, tear gas, mace, concealed weapon (article that appears harmless but conceals a knife/spike etc), Dypenylaminechloroarsone in all forms (can anyone tell me what that is), extendable batton, fighting knife ( butterfly, dagger, flick, push knives etc), hand or foot claws, knuckle duster, morning start, nunchakus, pistol cross bow, star knife, throwing knife, undetectable knife (made from material preventing detection by x-ray or metal detectors)