I happened across a little Firefox extension recently called Collusion, it shows who is tracking you as you surf the web all in an interactive node map. We all know that people cookie us and then track our wherabouts for advertising/behavioral data but I was really suprised to see so much activity is generated in 24 hours.
Here is the snapshot of all of the locations tracking me in one 24 hour period (keeping in mind that this only represents my work laptop, it does not include home and iPhone). I don't know about you, but I find this pretty scary. I know there is a lot of benign cookieing going on, but still, this is a lot of information being recorded.
Every node represents a different company tracking my behavior in a single 24 hour period. Online time during this period, 10.5 hours.
If you want to see your own map, get Collusion for Firefox here.