Been actually getting a lot of questions about this lately, think I'll write a post on it. But here's a short summary: Example I was creating a product in women's apparel so I would go to a bar, find a group of women, and buy them a round of drinks, the women would talk for hours about the subject (as an added bonus it also helped the social life). Don't underestimate interacting with the customer and seeing how they use the product. Instead of asking, do you like this, find out why and how they come to their decision.

When I do web products, the UX, I'll create a wireframe/mockup then find people and ask the question, "How would you do X". Then see how they think through the interface. After a couple iterations I'll create a quick web app to test varying hypotheses.

Another tip, I do this when forming a pricing strategy, is to form a few cases (X price with Y features). Then see which the person picks or test one at a time and see which gets the most responses. You can do DOE or multivariate analysis and come up with a near optimal solution.