If you are a permanent resident, you are not a Thai citizen. You still can not own land in Thailand and will need a work permit for working. But permanent residency will grant you some benefits:
When you are granted permanent residency in Thailand, they gave you a document explaining some of these benefits:
To be honest, the benefits are minimal because you will still have to report to authorities once in a while (see below). But once permanent resident of Thailand, you can apply to become a Thai citizen according to the law. You can normally apply for citizenship after 5 years or permanent residency.
You can normally apply for permanent residency once a year, around December. The ministry of interior will issue some announcement each year for the opening of the permanent residency. There is a quota of granting of maximum 100 people per country, decided by the ministry of interior. To cost to apply is only about 7,600 baht (update in December 2014). But if you are granted permanent residency, you will have to pay around 191,400 if not married to a Thai, if you apply under share or preferred investment, expert, employment, or not married to a Thai person or 95,700 if married to a Thai to get the certificate of permanent residency.
(fees should be mentioned here: http://www.immigration.go.th/nov2004/en/base.php?page=fee)
There are different categories like:
If you are approved, you will receive a blue book. Then, you have 7 days to go to the police station and get another book, a red one. After, you must register your place of residence in Thailand at the registration office (called "amphur" in all provinces or "khet" in Bangkok) to get a house book, or Ta bian ban.
Your permanent residency never expired. However, every 5 years, you must go at the police station of your area and stamp your book. And you can't leave the country for more than 1 year.
On top of that, if you leave Thailand, you need to apply for a re-entry permit.
Isaan Lawyers has applied successfully for permanent residency in the past. Here's the story of the Managing Director of Isaan Lawyers, Mr Brousseau, who has permanent residency:
If you wish to apply, please send us an email. A lawyer will not speed up the process: be aware that it is a long process that can take years. But we can help you to build a nice application to raise your chances of success. Immigration has a point system and you must get 50 points to be granted permanent residency. We understand how they proceed and can help you about that.