I see this argument/question come up all the time in a variety of different contexts. Inevitably it boils down to some form of "this company/site/person is taking away my privacy!" Typically this stems from the belief that a particular practice deployed at a company like Google forces you to give away information about yourself to use it, thus breaking off pieces of your "privacy".

But let me clear something up. You have no privacy if you use the internet. Not one ounce. There are numerous companies that have data warehouses of information on every single person that has ever filled out a form on the web. I'll actually go as far as to say I believe some of this information comes from brick and mortar sources... even Doctor's office or grocery stores, for instance.

How do I know this? I worked in the affiliate networking industry for a few years and one of the tidbits I discovered is a company called Targus (http://www.targusinfo.com/). For $0.50-$0.75 you can lookup anyone's information via API. This includes things like name, age, location, phone, employer (I think), salary etc... As a developer we were implementing this for our clients and one of the developers opted to look himself up. The children count returned 2.5. He does have two kids and at the time his wife was 6 months pregnant.

The bottom line is your privacy was most likely stolen a long, long time ago and any feeling of giving it up is really just an insignificant personal emotion.