I don't know if it is going to kill off AAA because kids don't buy them. There is a good chance theywantto consume the games but simply lack the funds. They'd prefer to see and experience the game with someone else controlling it than pop down all their monthly allowance money on purchasing it proper. So my argument would be when they have less free time to watch people play the games and more disposable income to buy the games they'll switch paradigms. I'm sure if these Lets Play really cut into the sales (I'd imagine they bolster sales actually) there would be massive litigation by the game giants to get them shut down. Not to mention the game companies freely give the games away to the popular Lets Play people pre-release and everything. So I think it would mostly be viewed as win/win for both parties.