When I first came across this expression, when I first arrived in WordReference, I thought it was really strange. It seemed to me to be a way of saving effort. "I'll include thanks in advance so that I don't have to give thanks when I get an answer." Since then, I have come to realise that it is meant sincerely, and that thanks are also (usually) given for the answer. But still, it seems strange to me, and I am certain I have never used an anticipatory thanksgiving in any letter or e-mail I have sent. I am now wondering if this is a cultural phenomenon? Is it something that I don't do because of where I live? Is it something that I don't do because I am me? Would you usually say "Thanks in advance," where you are: ... in business communications, ... in personal letters, ... in e-mails.