I stumbled across an old copy of Critique magazine, which Heather had left at our office, and came across a fascinating article about the design of the United States Census forms. The article covered the design process of the forms and explained the amazingly extensive user testing that the design team performed to judge the effectiveness of their designs.
One particular test was especially enlightening. Having as many people as possible complete the census form is of course very important to the census people. The design team first tried an approach that explained to people how important the census is to the country, thus encouraging people to complete the forms. This played very well to focus groups when they were asked their opinions, but when sample forms were sent out the results weren't encouraging. On the other hand, the designers tried a hardline approach that emphasized that completing the forms was your legal responsibility and you could be prosecuted for not completing them. People didn't respond favourably when asked in focus groups, but in test mailings (and in the actual census) the results were overwhelmingly successful. It's a good lesson that can be applied elsewhere.
As a side note, it appears that Critique ceased publishing a while ago. Too bad, it seemed like a good publication.