As for efficiency (no overhead for distribution etc) I don't really understand why do companies waste resources on technical measures of copyright protection in the first place. Almost every program which is even slightly popular has a crack/keygen anyway, almost every movie is ripped anyway, business users (pirating is more dangerous for them + they often need support) pay anyway (even if the activation form would accept any random string for serial), most of the users who download pirate copies would not buy a legal one (usually because it's hard for them to afford it) anyway (and that's how software like MS Windows and Office monopolize markets in developing countries where everybody just uses a pirate copy). So why to invest so much resources in DRMs, activation, genuine disks etc?