If you really want miles you might like to look at some of amazon's competitors - specifically Barnes & Noble which gives miles / points with Alaska, Aloha, American, America West, Amtrak, Continental, Delta, Northwest, United, Globalpass, Marriott, Priority Club, Airmilesmart, Clickrewards, Goldpoints, Greenpoints, Mypoints, Phonehog, Ebates, and Upromise.

FYI On my site Care2 doesn't award you anything but insteads makes a donation to charity based on your purchase.