Perhaps a BL'er with extensive travel experience could compile an index of countires to be particularly weary of, such as Indonesia, Singapore, the UAEs etc?
I'll do my best with the SE Asian countries i have gone too.
SINGAPORE: You won't ever be asked to buy drugs here, nor have I seen any indicators of people on drugs at night clubs. I know a few singaporians at uni, and they tell me that undercover officers regularly patrol nightclubs on the look out for drug users. although some people do use drugs in Singapore, use is largely frowned upon and many locals would consider it far to risky. Singaporians are sometimes drug tested at Changi airport after arrival from overseas, if they are found positive for drugs they can be arrested for having drugs in their system. Sentences for drug use and possession are severe. when arriving on a singapore airlines plane you are reminded that drug use and trafficing is punishable by the death sentence. Out of all the countries in SE Asia this would definately be the one to steer clear of drugs.
THAILAND: drugs are definately available, and you will be asked numerous times if you want to buy them at places like the Islands. Marijuana is pretty prevlent. As is methamphetamine. Mushrooms is probably the safest drug to do as it is often sold in shakes at certain places on the beach, and they pay off the cops so they can sell them and so they can be consumed at the bar. However, sentences for drug possession and use are severe and can mean years in jail for possession. Large quantities may incur the death sentence. Though bribary is a possibility it is not always easy or possible. Small amounts of marijuana will at least be a couple of hundred dollars, ecstacy is over a thousand. if you can't pay you'll go to jail.
VIETNAM: drugs are very prevelent and if you are young and not asian you will be asked constantly, particularly by motorcycle taxi drivers. The main ones are marijuana, opium and heroin. The quality of alot of marijuana is rubbish, the opium is nice. Drug penalities are severe like thailand, and they have the death sentence. bribary is a possibility. For the most part I steered well clear of drugs with the exception of buying some opium once. BTW, Vietnamese police are a different breed of scary, I wouldn't want to have anything to do with them.
Laos: Alot more drug friendly than the previous countries. Drugs like opium and marijuana are regularly offered. In some resturants and bars you can buy food or drinks laced with weed, meth, opium or mushrooms. There is less police presence or enforcement comparative to the previously mentioned countries. However, as like the other countries if you are caught it is a lengthy jail sentence plus they have the death sentence also.
Cambodia: probably the most drug friendly of them all. Little police presence compared to the other countries, and minimal enforcement (its a pretty lawless country fullstop). You get asked constantly if you would like to buy, to the point of it getting really fucking irritating. Bars, resturants, guest houses all seem to either sell over the counter or have dealers that will hassle you non stop. Everything is prevelent, and don't be surprised if people try to push smack and ice on you hard. As with the other countries if you are caught and can't bribe, the sentences are severe and they have the death sentence.
Also, a final word of warning. Apart from the possibility of spending long stretches of time in a third world jail, for people who use smack, be very careful as the heroin in these countries will be very pure compared to what is in Oz. further, steer clear of 'cocaine' I have heard reports that in SE Asia it is often heroin.