If you can't imagine anything bad happening, you lack imagination.
Assume Amazon will lose your data. Assume everyone else (facebook, twitter, g+, flickr) will lose your data, give them up -- or that they are already public.
Assume someone will correlate all that data, and sell it as a black market service to allow anyone to track you, see if you're in or out of your house, assume your government will put you on a no fly list if you're buying books on military tactics, left/right wing political opinion, assume your government will become oppressive in 15 years and mark up all your kids for "special attention" based on your shopping habits today etc etc...
Assume Amazon will lose your data. Assume everyone else (facebook, twitter, g+, flickr) will lose your data, give them up -- or that they are already public.
Assume someone will correlate all that data, and sell it as a black market service to allow anyone to track you, see if you're in or out of your house, assume your government will put you on a no fly list if you're buying books on military tactics, left/right wing political opinion, assume your government will become oppressive in 15 years and mark up all your kids for "special attention" based on your shopping habits today etc etc...
See also:
"The Right to Privacy by Louis Dembitz Brandeis and Samuel D. Warren" http://www.gutenberg.org/files/37368/37368-h/37368-h.htm