Here is an interesting site.
One of the things I'm pretty good at is measuring interest. As in, it's the foundation of just about all my skills save programming itself.
All humans have a knack for "reading" other humans. Some people don't excersize that knack, and others have unusual skill. But when we look at someone, chat with someone, or watch someone, we learn a lot about them.
There's a meme going around that it's "bad to judge by appearances" - it's a twisted mutant offspring of the "equal rights" meme. That's bullshit. You can, do, and should judge people by what you see, hear, and smell. Sure, you shouldn't assume a black person has whatever qualities you might assign black people, but if you see those qualities, then that person has those qualities, whether he is black, white, or heliotrope.
I'm rather adamant about this, because I'm really good at it, and each year I realize I'm twice as good as I was the year before. I catch a lot of flak from people, largely because I'm totally tactless. However, I can't ever remember being wrong about someone's personality. This is what leads to my harsh dismissals, my arrogance: I can tell what you are like, what you are interested in, and where you are in your life. More importantly, I can tell whether or not you'll ever get anywhere.
Is it "private data" that I am collecting? If I can clearly tell someone is having a rough time at home, or that someone is gay, or that someone is a clear credit risk, am I "stealing" this information?
Of course not. It's publically available information. I just happen to pay more attention than others.
Similarly, AttentionTrust's assumption that your attention is "private information" is total bunk.
Of course you should have access to that information. But you do. You're making all the choices. While you do these actions in public, whoever you are with (say, Google, or perhaps whoever's page you are surfing) can also see these actions. And, if they want, they can tell anyone they want, the same way I could say, "boy, Joe looks like he's in a bad mood today" or "did you notice Sue likes horses?"
I am not required to tell you that I know you're having a bad day, or that I figured out you like horses. And neither is Google or anyone else. In fact, many people make very good money by telling you what they figured out about you. Or pretending to.
Providing you with a method of tracking your own attention is great, but the idea that people are somehow doing something immoral by noticing what you do in their front yard is bogus.