Street-smart companies have borrowed an idea from former New York City mayor Ed Koch, who used to wander around asking his constituents, "How'm I doin'?" The companies send customers a large envelope containing three pieces of blank paper, a pen, and a self-addressed, stamped envelope, along with a note asking the recipient to "take a moment and write down what you really think about our products and our service." The companies report they get some very revealing feedback -- the kind of feedback more traditional customer surveys just don't pick up. A few practitioners even claim they can trace a rise in sales directly to the mailings.