Yes, people actually fall for this stuff. To make someone fill these out, they must be concise and visually appealling. A person filling these out cannot be hasseled with difficult choices. Check Boxes are also a nice effect. These must look believeable.
Credibility is everything with social engineering.
I cannot stress that enough. I will soon realease examples, although you should be original and make some on your own. Now, after stamping and addressing your letters, send them out and wait. Soon you should receive some answers. At this point, use a standard phone social engineering.