One effect of digital books that I don't remember seeing discussed anywhere

Several (many?) major publishers have mass-market paperback public domain lines. These books don't generate a lot of revenue each, since they're usually sold very inexpensively, but they also don't cost a lot to make, and they are capable of selling a great many copies each. (I don't think I'm giving away any secrets when I mention that Tor Books's 1992 edition of Bram Stoker's Dracula sold significantly more copies than Signet's novelization of the movie, Fred Saberhagen's Bram Stoker's Dracula.)

However, as reading e-books becomes more of the everyday habit of reading, what happens to these public domain lines? I can't imagine they'll go away completely, not for a very long time--but they'll definitely be hurt. It's hard to compete with free.