... and then prepared to be disappointed, for it's not all that Earth-shattering.
Yes, Google tracks your behavior as you navigate the web. And so do thousands (maybe only hundreds) of other online entities. And if you're shocked by that, you're either not paying attention or new. If the latter, welcome to my site. If the former, welcome to paying attention.
Google, and lots of other sites, track you by something known as a cookie. It's not tasty, and diabetics shouldn't worry. A cookie is a nothing more than an identifying tag that gets associate with your browser. When you browse to different websites, websites read and set cookies all the time. Cookies do not pass personally identifiable information. Anyone who tells you differently is incorrect1.
Yet this still weirds people out. They worry that some straw man, let's call him Big Brother, is collating all these cookie entries, web history and other data to actually figure out who you really are, for some unnamed yet nefarious gain. And to that I say: balderdash.
Some time ago, Google got sick of everyone freaking out what they did and didn't know about you. So now instead of sweating that Google is telling a host of advertisers about your predilection of visiting some er... well, unsavory sites you may have stumbled across but quickly left when you realized what it was honestly it was only that one time I'm a good boy I swear... now you can just check to see what sorts of interests Google thinks you're into.
My list is shown in this post. If that's all they have about me, you probably have nothing to worry about. I'm online all the time. I visit lots of sites I probably wouldn't want my grandmother surfing to anytime real soon. Yet those don't show up. And the categories that do seem a pretty close approximation to my interests.
Personally and professionally, I think that highly targeted ads do make for a better online experience. Notice I didn't say that ads make for a better online experience. They are a fact of life and won't go away. So if I have to look at the damned things2, they might as well be as targeted to me as they can get.
So the bottom line: don't be scared. And don't jump to conclusions. At least that's my $0.02. If you have a differing opinion, that's what the comments are for. But please, no crazy conspiracy theorists. If that's your thing, go bug my friend Phil. He digs that sort of stuff. :)
1 - Yes, it is possible. I'm also willing to concede that it may have happened in the past. But there are enough privacy watchdogs fighting the good fight that I sleep soundly at night.
2 - Yes, I realize there are plenty of ad blocking programs or tweaks available to me. They aren't worth my time. They may be worth yours.