NVIDIA's partners have received permission to overclock its GPUs years ago and now manufacturers were able to finally persuade ATI to do the same for ATI based graphics cards.
ATI's partners have now finally managed to persuade big red to let them overclock. We are finally going to be able to get the faster-than-the-reference-design cards.
ATI will provide a warranty for such chips and there will be some kind of validation process where ATI will be able to control the overclocking frequency. After you sell your chips you kind of have to give the warranty for them.