A UC Berkeley report provides an in-depth look into the Internet Privacy issue and to what amount you are really being tracked ... several media outlets have reported on this issue. Register | NyTimes | BizJournals All with their own take on the report ... a few key excerpts from their study ...
Dominance of Google
"From our analysis, it is apparent that Google is the dominant player in the tracking market. Among the top 100 websites this project focused on, Google Analytics appeared on 81 of them. When combined with the other trackers it operates, such as DoubleClick, Google can track 92 of the top 100 websites. Furthermore, a Google-operated tracker appeared on 348,059 of 393,829 distinct domains tracked by Ghostery in March 2009 (over 88%)."
This is one of the main reasons why the majority of these "trackers" are included in the MVPS HOSTS file ...
"Among the top 100 websites" this was obtained from Quantcast ... however the "Top 100" are not really individual sites since many are owned by the same company ... so you can see how these big companies can compile quite a lot of info ...
[Example of the Big 3 - ranking]
microsoft.com (7), live.com (3), msn.com (4), windows.com (19)
Not counting their ad servers: Atlas DMT (atdmt.com) aQuantive (adbureau.net)
google.com (1), youtube.com (6), blogspot.com (14), blogger.com (40)
Not counting DoubleClick which ranks #37 at Alexa
yahoo.com (2), flickr.com (30), geocities.com (47)
Not counting their ad servers: Overture, RightMedia, BlueLithium
"Websites make distinctions between sharing with affiliates, contractors, and third parties. Of the top 50 sites, 29 stated that they do NOT share user data with unrelated third parties. However, 45 affirmatively state that they share data with affiliates, and 36 affirmatively state that they allow third-party tracking. The average consumer might assume an affiliate or tracker to be a third party, but given the actual usage of these terms in privacy policies, that assumption would be mistaken. Of the top 50 sites, 43 state affirmatively that they share data with third-party contractors, including all 29 of the sites who state that they do not share with unrelated parties."
This is why I recommend turning off Cookies and "whitelist" (allow) only those that are needed ...
NO ACCOUNTABILITY FOR THIRD-PARTY TRACKING
In the Register article they state: "Omniture and Quantcast cookies appeared on 57 per cent of the top 100 and less than 6 per cent of the 400,000" ... I would offer that this figure is actually much higher, since Omniture (112.2o7.net) also makes extensive use of clones to disguise their 3rd party trackers ...
om.symantec.com is actually symanteccom.112.2o7.net
std.o.webmd.com is actually webmdglobal.122.2o7.net
stats.adobe.com is actually adobe.com.112.2o7.net
Using the Register as an example you can see the extent of tracking from third parties that goes on ...
I'm not sure what grade level 17.29 is ... but I'm sure I didn't go to school that long! ...