The big problem in Thailand these days is overcrowded roads. But it is still possible to get away from it all. I have always really enjoyed the drive down to Phuket and there are some great mountain roads to the north.
Police are an issue in Bangkok. I've been stopped a couple times. They are corrupt but I have a general policy against paying bribes. So I've had to surrender my IDP a couple times. Probably still waiting for me to pick it up somewhere.
Outside of Bangkok there really are no rules. I've never once seen a speed trap. That's the beauty of Thailand. It really is lawless.
It isn't the sort of place you can cruise at 250 km/h. There are few roads that are suitable for that. But some of the roads never stop winding. Driving standards are competent but agressive. The truckers will help you pass for example by indicating to you that it is clear ahead. You always have to be careful though. The old back-packer saying is never take a bus on a Thursday because the driver will be too busy watching the kick boxing to pay attention to the road. I've many a time found myself stuck in traffic three abrest on a regular two lane road with everyone jockying for position to get past. As I said, lawless but fun. You have to use caution as it is an excellent place to get yourself killed.
Oh, and you also need to be careful of the mopeds. They're unlicensed and don't really have enough experience to understand the speed of the cars so they will sometimes cross in front of you without looking. No need for mirrors.
Also, if you take your Turbo there you have to be careful to make sure that it doesn't end up a share-Taxi in Cambodia (picture your car with the back window removed and about 14 people in it with people sitting on the roof and sitting in the back window and sitting on the door sills ... well you get the idea).
It is a while since I did it but taking a car over the border is pretty easy. You need to sign something in Thai promising to pay about $1M is you don't export the car again and then you are free.
Language, road signs, etc. never seemed a big deal. If anything, inability to communicate is a form of protection. No one at a road-block will ever bother you.
Have fun!!
S.