Yep, the GF and I have been all over Thailand on the trains. Will be going again soon to Vientiane, Laos and back.
The only problem we had was a couple of months ago on our way from Hua Hin to Singapore.....on the Hat Yai to Butterworth section the aircon in our car was DEAD...felt like we were slaves being transported to a work camp. (sweatin like a farm animal). And the train was FULL, so no moving to another car.
We got off in Butterworth, and luckily were able to then buy a 1st class ticket on the same train. The next guy in line, who was in our car was not so lucky; he had to wait a few hours for another choo choo or get back on the slave train.....he decided to wait.
For the GF and I, if the trip is over a few hours, I think that 1st class is well worth the extra money.
Also, take a roll of duct tape if going first class.....the aircon can get downright cold and make for a sleepless night......so I use the tape as a thermostat.
Also, here is a website that was recommended on another forum yesterday.
http://www.thairailwayticket.com/Defaul ... language=1
When Chuck Norris does a push up, he isn't pushing himself up, he is pushing the earth down.