So if you haven't done so already check out the rundown of discounted titles because it's a pretty notable bunch. (ps3attitude.com)
In exchange, they allow you to discount your title for five days, which increases your downloads and raises your chances of being on a bestseller list. (wiseinkblog.com)
So they can discount their titles more aggressively then the storefront booksellers. (koehlerbooks.com)