I came up with pretty much the same idea last week, and then I found Launch Rock [http://launchrock.com/] and left it behind... Hope it helps at least for comparing what you plan to what they have.
Do you think LaunchRock is good for testing products that don't exist yet and where the creator doesn't know whether or not he wants to make the product? For example, I want to see whether or not people would buy...a new type of skateboard I'm thinking of making. Do you think launchrock would work for this?