Worst case, Apple starts dropping a free bumper into every iPhone 4 box and has existing owners drop by genius bars or enter serial numbers online to receive free ones. The bumpers probably cost Apple a buck or less, so it won't kill them. People will still buy the other bumper colors even, just to differentiate themselves from the boring, free one everyone has. Nintendo having to offer free replacement wrist straps for early Wii Remotes didn't hurt that system any.