What is the purpose and what are you trying to achieve? I think think that a common thing is to authenticate a user and show information from his/her facebook profile. To authenticate a user using facebook you need to create a small facebook application and use the API keys from that app. Look at the documentation on http://developer.facebook.com
Login using facebook or twitter account. Is this possible in EPiServer?
If it is, who owns the information (more of a privacy issue), Facebook, the site, or both?
Thanks.