I'm assuming that with googleanalytics script running on 3/4 of the websites I visit that they're also gaining a ton of data from a lot of your behavior online. (I have scripts and ads turned off, except for certain sites such as this one.)
What I found amazing was that my wife was looking at some product on one of my computers. Half an hour later, she was on her laptop in the living room. She started receiving ads for that product on her computer. I don't know if she had "temporarily allow all of this page" turned scripts off or what; but 'they' still managed to track her behavior by IP address.
Ghostery makes it interesting. Google shows up everywhere. You've got their datacenter standing behind you most of the time you're online.
Google Analytics is here at the forums.
Head to Wallgreens.com to check on some medication. Doubleclick is there. (Doubleclick is owned by Google.)
Check news at NPR.com or Foxnews.com - Google and Doubleclick, respectively.
Look at cat pics at Reddit or Tumblr. Google is there.
Watch gory car crash videos on Liveleak. Google again.
Check investments at Edward Jones. Again.
Post racist rants at a KKK forum. Google and Doubleclick wonder about your choice of friends.
Read up on heart failure at WebMD. Despite your choice of forums, Doubleclick hopes you're feeling ok.
See what you can do about student debt at
www.studentdebtrelief.us. Mhmm.
Two sets of footprints in the sand. Google's datacenter was following me. Then, when there was only one set of footprints, that's when I installed Ghostery and Cookieculler.
i agree. i couldn't care less if they know what websites i go to or what i enjoy, then try to market towards me. i don't see most of it because of adblock anyways.
You're easier to manipulate than you'd like to think though. Annual spending on advertising is
in the hundreds of billions of dollars about $170 billlion.

They're not doing it entirely because they like being attention whores. They're expecting a return on their investment. The more they know about you, the more manipulative their ads can be, tailored to effectively coerce you into handing over money.
Marketing is surprisingly effective.
correct, i do not give a shit. they are scanning my email and billions of other people's email. my info is a needle in a haystack. no ... more like a needle in a billion haystacks. not really concerned.
also don't give a shit if the government is doing the same.
just because they have all of this data doesn't mean anyone is looking at it. and even if they are ... meh, don't give a shit.
"Needle in haystack" analogies only really work on people and sluggish computers. What if you've got a computer that can analyze those billion haystacks in a few minutes and not only sift out the needles but also count the individual pieces of hay and produce a graphical distribution of their lengths?
Along those lines,
here's something quite sophisticated which is performing a relatively trivial task: Sorting "bad" potato chips from an assembly line. It can visually inspect
5500 pounds of potato chips per hour for a variety of defects, and then automatically remove them from the conveyor belt. There's that level of technology at work to help keep the horrors of overcooked or bubbled potato chips away from customers. It can also detect foreign objects, such as insects, rodents (or rodent pieces), stones, stems, and perhaps even small pointy pieces of metal.
Imagine what you could do with Google's amount of money, especially if you're not analyzing physical objects.
So, "needle in a haystack" only works up to the point that you are facing a high-speed haystack-inspection machine that's been optimized for needle detection.
(Seriously though, that's an impressive machine.)