OkCupid was really well thought out for making matches for relationships. The double connection nature of the questions that allowed not just answering questions but also what answers you'd accept and how strongly you felt about those answers was great. It also did a nice job of sussing out people's true personalities. The more questions they answered the more difficult it was to hide their true selves. One of my favorite examples of this was a question about why birds don't get harmed when they land on power lines. The question could be used to gauge a person's technical knowledge but the answer "They do but they express it poorly" was a signal of a sense of humor. Lots of questions were variations on each other but written differently which is another way of getting to a person's true core.