They should be releasing demo discs when consoles launch. This way gamers have an idea about what is to come, and they can share that with their friends, and spread the games. It also gives variety to the games you can play because at launch dates there aren't man mega-hit titles.
About releasing them now. They better do it at a cheap price, or I can pretty surely say people won't buy them (unless if they have some real big games in there).
Also, the new Gamecube buyers are soo lucky. $150 for a Gamecube, Free Game, and now a Demo Disc.