I liked it better when the web was impersonal, when you actually had to make an effort to filter out the information you didn't want. As more and more of the top of your search results get cluttered with things that Big Bro knows that you want, the less and less you are exposed to the world of things that you never knew you might take an interest in.
Search used to be a way to find marvelous new gems in the ocean of Internet. Now it's just a reaffirmation of your favorite repertoires, leaving you with the ultimate confirmation bias in everything you read, buy, and think about. These days, I can rarely find anything with Google that I didn't already know about, read about, write about, etc. Half the time, I use Google as a bookmark manager ... heck, I might as well just search my browser history. Throwing email history into the mix will only accelerate this trend, shoving each of us even deeper into our own little holes in the ground. Search has become boring, an incubator for egocentric brats, and a place where political diversity goes to die ... all in the name of personalization, i.e. ad revenue.
Nowadays, the only sites that dare to give me non-personalized information seem to be DuckDuckGo and Wikipedia. Oh, and occasionally Google, when I'm logged out and freshly rid of cookies.