When you're visiting a site with a +1 button or a Facebook "like" widget or an Adsense advertisement, you're not (knowingly) choosing to use Google or Facebook.

When you're visiting a site with a +1 button or a Facebook "like" widget or an Adsense advertisement, you're not (knowingly) choosing to use Google or Facebook. Isn't that what this is about? Third-party cookies? In principle, having a site declare its practices might not prevent you from being tracked, but it might result in legal consequences or bad publicity for the site in question. Not every problem has a purely technical solution.