Is "unfriend" a word?

The 2010 AP Style guide, "the essential tool for writers, editors, students and public relations specialists," according to its website, has just been released. This reference is used to determine such things as what new terms are acceptable when referring to social media. In it, "friend" and "unfriend" are both verbs. I don't know about you, but we regularly disagree on this point in my house. Other terms found in this edition include app, e-reader (still gets the hyphen), and flu-like.