The direct marketing discipline is often described as the most effective medium in terms of correlation between ad budget and sales. Personally I rarely find myself being affected by the mails that lands in my private mailbox.
Then the other day I was somewhat surprised to see that a contact from my bank had written a little poem as an intro to a request about finance for a new car. It was about dreams and discontent with my current life. All good questions asked but probably not something I would discuss with a man I have never met unless he had a psychology degree or something.