^&^^ I seem to remember a fairly well known poster on the thai forums saying that he was reciving interest, and the bank noticed and then deducted it all from his account, in one go. A couple of years worth.
I once opened an account at bangkok bank, and as I was leaving I was called back to the esk where they quickly scrapped the book and card they had given me an started again. It seems they opened the account an designated the wrong "code" or something like that. It seems that there is a code for foreigner accounts which triggers the system not to apply any interest. I got the lay to confirm this at the time.
Maybe this has all changed because it was about three years ago now. Just looking at my bankbooks now for accounts at Bangkok Bank, Siam commercial bank, neither accounts have ever paid any interest during the last 4 years an both are designated as savings accounts Racist #&$&$^^*[at]*[at]'s!