Finally, I picked up the beautiful immigrant visa from the US embassy in Bangkok. Many thanks to those who share their views with me. Now I'd like to know the procedures at Los Angeles POE.
What do I have to do at POE ? How long does it take ?
At the POE after clearing customs you'll face an immigration official. He/she will direct you to the secondary inspection room where your envelope will be opened and visa examined. After that you'll get an I-551 stamp in your passport and become U.S. legal resident. The whole process will take minutes. After that you'll get emotionless "Have a nice day" and will proceed to Arrivals area. Plastic card will arrive in the mail in a few weeks.