Perhaps they aren't publishing non-anonymized data. But the fact that they are collecting and analyzing these data without any kind of opt-in system is a little disturbing. If they're willing to do that, how willing will they be to protect these data from falling into the wrong hands, especially if the "wrong hands" are holding a warrant or a court order? I'm sure glad I don't have a highlighted e-copy of, say, the Communist Manifesto or the Anarchist's Cookbook. I wouldn't know who to expect knocking at my door.
Do you honestly think anyone cares what you highlight in the Communist Manifesto or the Anarchist's Cookbook?
Even presuming some dystopian future where The Government (cue hammy antagonist music) is busting your chops for what you read, the fact that Amazon has a receipt for you purchasing a copy is likely to be a bigger deal to them than which bit you highlighted.
"Some dystopian future"...like the U.S. in the 50s, when Joe McCarthy was demanding the removal of material he deemed "inappropriate" from State department libraries? (Wikipedia says some libraries actually burned the banned books: http://en.wikipedia.org/wiki/McCarthyism#Senate_committees) If that sort of suppression is possible in the U.S. when private companies aren't holding vast amounts of data on exactly what "subversive" material citizens are reading and finding important, what's possible when that information is easily accessible and searchable by anyone with a government order?
Not all of Amazon's customers live in the U.S., either. It appears that they don't currently sell the Kindle in Iran and China, for example, but if they did, I sure wouldn't want to own one there.
Someone definitely cares about what you highlight in the Communist Manifesto, if you are arrested for a crime. Why give the authorities fodder to build their case?
