I've stayed in Thailand for extended periods and stayed in some out of the way locations in the 'jungles', I was even a monk for a while there. I have only been sick once and that was from eating food in a restaurant in bangkok.
The things to look out for are hepatitis which you can get from sexual and non sexual activity, tetnus - from rusty metal, rabies from dog bites etc. There are heaps of dogs around and most do not pose a problem, but some do and you could be bitten. So getting shots is good. Malaria is not really a problem there and I have never taken any tablets etc.
The main dangers are non medical I think. Accidents are a serious problem. I would suggest you never ride a motorbike there, or even drive a car. Police are a real problem too. Expect to pay bribes - although it would be an offence in Australia to bribe a foreign official. If you get into any trouble just pay up asap. One mate go into trouble for putting a cigarette out ina flower pot and was arrested - he quickly paid the 500B fine and was let go. If he didn't he would have been arrested and taken to the police station and made to wait while they processed it for hours, and still would have been fined anyway.
Prostitution is rampant. If you want to participate then be careful. Drugs are also very common and best to steer clear. The prostitution side is interesting and even if you are not into it it can be good to go have a look at Patpong in Bangkok. Its a real eye opener.
There are also a lot of weird westerners there. Any criminal on the run appears to head for Pattaya - which is one big brothel with sand. There are heaps of Russians there now, bikies, gangs of ATM theives, tattooed bald guys etc. Amazing place, but best to stay away I think as there are heaps of better places.
And do not comment about the royal family there as you can be easily arrested and sent to prison for up to 15 years - there is many recent cases including and american citizen who translated parts of a book about the King (published by Yale university press too) which is banned in Thailand. He arrived in the country and was arrested and jailed for 15 years. The King is 84 years old and when he dies there are going to be huge issues - see the recent happenings in North Korea.