I actually really like that model. Anytime I download a free game I understand that there will probably be ads. The developers put a lot of work in to the game and they should be compensated for their work. However, games that provide an incentive to watch the advertisement are doing it the right way in my opinion. I would love to see some statistics on advertising revenue of systems that give an incentive to users to watch ads vs. systems that force ads on their users.