The Filter Bubble is an outstanding book--a compelling and important argument, delivered persuasively through real reporting, analysis, telling anecdote and hard data.
One of Eli Pariser's central points is that personalized internet services--Google, Facebook, advertising--can put you into a "you loop", in which they show you what you think you want, and then you wind up wanting those things more because you see them more often. Invisibly, your momentary impulses (click on this, ignore that) shape your reality, and your reality shapes what you respond to.
Since reading the book, I've found myself compulsively testing one of its main case studies: Google's automatically personalized search results. Try searching for "guns": I don't see the NRA on the first page, but friends do. Huge differences on "abortion" too: some people see Planned Parenthood, other people see Catholic.com. Even searching for "bias" shows different results to me vs my wife!
Drawing on history, academic research, exclusive interviews, and a huge range of other sources, the author takes a hard look at the algorithms that increasingly shape how all of us think. He contends that unchecked profit-centric personalization threatens democracy. When you read the book, you'll come away convinced. And you'll appreciate how the book itself makes our democracy stronger.