I dont think starbucks advice is that terrible. Even though mechanicle turk does seem like a good alternative, I would much rather go to a coffee shop or a bar where I know startup savvy people hang out and discuss it in person. But one of the best advice I ever received is - Start a blog and gain some traction for it before you launch your MVP. Discuss customer stories and problems you are looking to solve. Ask people opinion about your solution, discuss/debate in public. Use these discussion to keep on refining your direction and feature set. As a positive side effect you might end up creating a passionate community around your solution before launching and have list of people interested in paying you money beforehand.