I have been learning Thai for about five years now and can speak, read, and write at probably an intermediate level (mind you the Thai books I have seen aimed at advanced learners in my opinion are only intermediate).
I live in a Thai village with no other farangs nearby and so I am forced to use Thai everyday. My wife can speak good English but none of my Thai friends can hardly speak a word. They actually speak the issan dialect of Thai here, even though we are in North Central Thailand (Phitsanulok). When I moved here two and a half years ago my Thai improved a great deal but a few months ago it plateaued.
I have found that by getting rid of all the English speaking channels on my UBC it has forced me to improve again. Most of these channels were rubbish anyway and they were all full of repeats. I now also have an excuse for watching TV as it is now a learning experience and I actually enjoy Thai TV. I am also saving 2000 bath a month.
I think that many Farang who stay in Thailand lose their motivation to learn Thai after living here a few years here. Which is a shame. I think that it is good to try new things to keep the interest going. My next plan is to give up reading novels in English and only read Thai ones for a while.
By the way, I think that anyone who says they can speak Thai after only a few months and that the tones aren't important is talking through their arse.