well wiki is popular because they have User generated content and it's really quite accurate and because they have set it up to be extremely user friendly, people just used it.
If you're doing a discounts website, I've got a friend who is working on one and it's very intensive.
after 18 months online I want to say to start by building a list. Start by collecting names for a database of people who are looking to get your type of discount service...
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