An intro to BitTorrent

You have a great product, many customers, and are delivering your product to hordes of happy customers online. Serving large files creates problems of scaling, flash crowds, and reliability. As you grow, they become more central to your business, but your bandwidth costs go up as well. It's a vicious cycle.
There is a solution. BitTorrent is a simple software product which addresses all of these problems.
The key to cheap file distribution is to tap the unutilized upload capacity of your customers. It's free. Their contribution grows at the same rate as their demand, creating limitless scalability for a fixed cost.

http://bitconjurer.org/BitTorrent/introduction.html