You don't have to install WGA to activate. You can actually activate without being connected to the internet by using the phone option, WGA is needed for Media Player 11 and a few other bits from microsoft, though, but seeing as this is a MCE box you should be fine with just activation. But to answer your original ?. If you continue without activation, you will get a pop-up every now and again telling you how many days you have left, once that time is elapsed, you will have to activate or you can't log in. I have never run a windows box past its open period so I am not sure if anything else happens.