Nothing. Nothing at all. So what is it, exactly, that will happen at midnight on the day CS4 gets launched that will make your G5 explode and your CS3 licence fly out the window?
Look, I get it, I can keep using my machine for as long as I want and I can keep using CS3 on it for as long as I want and my business won't be hurt. My main point is that large companies should not be willing to disregard and exclude their customers from the newest product launches after so short a period of time.