Google is in full swing for the identity war, without much fanfare. According to
John battelle, who runs an online ad business, Google recently changed their licensing terms and removed the sentence where it says they are not combining their data with DoubleClick's, a previous acquisition which uses cookies to track people online through ads.
There you have it. To do yourself anything good, you can either filter out all HTTP/HTTPS requests with doubleclick in it (and all the variations, such as doubleclk), and you can configure your web browser to delete all cookies after a session. Of course if you are using a mobile device, chances are you won't be able to do any of this.
Which means mobile devices are 1) a trap and 2) a tool of ultra-capitalism in all its incarnations (surveillance being one of them).
At some point, you will probably have to go online only when absolutely necessary and stay offline the rest of the time. Or, even more radical, take a hammer and smash those mobile devices of yours.