Authoritatively, Haberman writes:
Interestingly, ... From now on, the A.P. Stylebook — a bible of usage for multitudes of writers, editors and other species of word nerds — will recognize the legitimacy of the adverb “hopefully” as it is heard in everyday language, even if it makes a grammar stickler’s back teeth ache.
Undoubtedly, Miss Grundy cautioned you in the seventh grade that you must never write a sentence like this: Hopefully, the game will not be canceled. Uh-uh, Miss Grundy would say; never use that pesky adverb in so lax a manner. Proper English, she’d insist, requires rendering the sentence like so: He said hopefully that the game would not be canceled.
Truthfully, most English speakers gave up on that rigid construction long ago. Now, so has the A.P. Its message to subscribers noted that the traditional meaning of “hopefully” is: “in a hopeful manner.” But it added, “Also acceptable is the modern usage: it’s hoped, we hope.”Incidentally, Haberman notes that his newspaper, the New York Times, isn't planning to revise its restrictive use of "hopefully" any time soon.
But he concludes:
Frankly, though, the newspaper’s stylebook is not dogmatic on this score. As the new A.P. rule shows, times can change.I also need to update my advice for using hopefully in my online editorial style manual. It has noted the differing preferences for using hopefully. (I may have already made the change by the time you read this.)