The idea is brilliant; tap in to your users upload capacity to distribute your product across the Internet more efficiently.
If you have a killer product that your customers are downloading, the distribution (bandwidth) costs will increase proportionally with the amount of customers. This may be ok if the product is commercial and you can transfer the distribution costs to the cost of the product.
If on the other hand it is a free-ware product, lets say an open source application, you may find it hard to finance the popularity of the project.