> IE10 defaults to Do Not Track enabled. So sending the header is not explicitly representative of the user's wishes.

"By signing up for [insert service here], you agree to the privacy policy."

How many times did you actually agree with the privacy policy? Devil's advocate, I know, but it's a sobering reminder that pretty much anything you use gives information that is sold. Open a bank account? If so, notice any new junk mail? Pretty hard to live life without a bank account. Your information is still sold to third parties.