[nbm]

The purpose of the social plugins is to provide social context - telling you which of your friends has liked something, or that you are the first.

To do this, it needs to know who you are if you are a Facebook user that has not logged out. To do that, it needs to check the cookie that the Facebook web site sets when you are logged in.

Unfortunately, the web as it stands doesn't allow this interaction without divulging some information (time/date, browser, IP address, &c.) when the only interesting thing is who you are if you happen to be logged in.

This is the same problem that web analytics, certain comment systems, other social buttons, and other embedded functionality systems face.

About the best that can be done is explain what happens with that data when it is received - and that is explained at https://www.facebook.com/help/?faq=186325668085084

[bandushrew]

Dude, if I am a facebook user who has not logged out, they can send cookies as much as they like.

The browser manages this - if they are logged in, set a cookie that will be sent to the hypothetical 'like' subdomain of facebook, if they are logged out, remove the cookie.

This kind of functionality is really not rocket science, there are dozens of ways to implement it and I feel kind of stupid talking about it.

There are reasons for facebook not doing this, but they are not technical ones.