SAN FRANCISCO — Since the heyday of AOL’s cheery “You’ve got mail” greeting, e-mail has been central to the online experience for millions of people.

SAN FRANCISCO — When you sign up for Facebook, you enter into a bargain. You share personal information with the site, and Facebook agrees to obey your wishes when it comes to who can see what you post.

The nation’s top copyright official made a blistering attack on Thursday on a controversial legal settlement that would let Google create a huge online library and bookstore.