I've had a large amount of difficulty finding accurate, reliable information on drug laws outside the US, so I felt some sort of resource was in order. Since this is such a detailed subject, I shall be covering Australia state-by-state. NOTE: I am not a lawyer, all the legal information is from the Department of Human Services website and the Drugs, Poisons and Controlled Substances Act of 1981, incorporating revisions as of 1 January 2002. I advise anyone who is in real legal trouble refer to these original sources and obtain professional legal advice.
Merely using marijuana has the least severe penalties. In my experience, you are exceptionally unlikely to be charged, but even if you are the maximum penalty is an A$500 fine. However if you are charged, there will often also be other charges, such as possession, cultivation or trafficking. Possessing marijuana for personal use only carries a maximum penalty of A$3000 and/or one years imprisonment. Otherwise it's a maximum of A$40,000 and/or 5 years imprisonment. Cultivation for personal use carries a maximum penalty of A$2000 and/or one years imprisonment. If you're growing for the purposes of trafficking, there is a maximum penalty of fifteen years imprisonment. For attempting to introduce a drug into another persons body without their consent, there is a maximum penalty of A$3000 and up to one years imprisonment.
Okay, that's personal use done wih, now let's move on to the profitable part: trafficking. Unfortunately trafficking has the highest penalties of any marijuana related offence. Trafficking or cultivation for the purposes of trafficking carry the same penalty, which is based on quantity of marijuana. Up to 250 grams has a maximum penalty of up to 15 years imprisonment. From there to 250 kilograms the penalty is up to A$250,000 and/or 25 years in prison. Anything above that they can lock you up, throw away the key and fine you up to A$500,000. Possessing instructions or equipment for trafficking or cultivation for the purposes of trafficking carries a penalty of up to ten years of prison. Aiding or abetting in any of these activities, you are subject to the same punishment as if you had committed them.
For a police officer to obtain a search warrant, he or she must find a magistrate willing to sign a document stating that they believe the police officer that some sort of drug related activity is going on in the next 72 hours. They can confiscate anything they believe may be involved in aforementioned drug activity. In public places, police are fully authorised to search your possessions, vehicles and animals.
Well, I hope someone finds this helpful, or at least interesting. If I've missed anything or gotten anything wrong, drop me a /msg so I can correct it. I say again though, if you are being charged with any criminal offence, you should seek professional legal advice.