Reference materials as we once knew them are changing daily. It seems no one uses our encyclopedia sets anymore - they remain in pristine condition on the shelf. Now the book format of the dictionary is on its way out. One of the oldest and most prestigious dictionaries, the Oxford English Dictionary, weighing in at 130 pounds and in publication for 126 years - may only be available online. The current digital version gets 2 million hits a month from subscribers who pay $295 a year for the service.