To be honest, now when I see all that information that Google knows about me, it really is a bit scary :D… It knows how much time do I spend at work and how much time do I spend at home. It knows places I visited (Latitude), videos I watched (YouTube), music I listened (Google Music), web history (pages I visited and searched), people I contacted (Gmail), and that is not all :)… There are also some things which are not shown at the moment. For example, data from AdSense, Webmasters Tools, Google Analytics, Docs, etc. To see the whole list of data collecting services, check out this great article about how and which data Google collects about us.
Should I be worried?
The fact is that we don’t have to use Google, nor Facebook, nor any other data collecting service on the Internet, if we don’t want to. But, do we lose something by not using their services? Are there alternatives?