How many consumers should I interview for market research of a product?
pedalpete: I can't say I have ever done this for a physical product, so not sure how it differs, but why go in with a solid number? Why not use the feedback you are getting to adjust the product until you feel you've got it right.One really good thing to do is what (I think) Panasonic did in the 90's with a focus group on what color they should make their portable CD players. 
They brought in red, blue, yellow, green and black, and asked the group what colors they would buy, what each color represented to them, etc. Then, as the group was leaving, they were told they could take one of the portable disc players with them. 
Apparently, the focus group had voted overwhelmingly that the players should be red and blue (or something like that), but when the researchers counted the players at the end, most had taken black or yellow.If you can figure out how to get 'true' feedback, rather than getting your questions answered, then you'll be way ahead of the game.