WARNING: If Google is so wonderful and trustworthy, why is it that they track virtually my entire activity on the web? I don't recall them asking my permission. If you value your privacy on the internet, stay away from Google.
This is an official web site of Google.
For years, they have promised countless times they would never combine the data they gathered about you via all their services. But now, with the weak excuse they had "no other choice", they are going to combine all the data including your IP address, cookies, search terms, e-mails, social activities, location and whatever-the-**** you even didn't know yourself they know about you into an ultra-personalized profile. (As of March 12, 2012.)
They will now know who you are (profiles, Gmail etc.), what you do (docs, maps, Android phone), what you buy (checkout / wallet), what websites you visit (Google Analytics, present at many of the most popular web sites), who your friends are (Gmail, Google+), what you watch (YouTube)... You name it. They will use this info to serve you super-targeted ads. Only DoubleClick advertising (for 3rd-party web sites) isn't included in the list of services for which they are going to combine info. At least, for now...