The Radeon HD 8000s will probably launch sometime this winter. I haven't heard any rumors about the Geforce 700 series (apart from when the 600 series was mistakenly referred to as such), and my guess is it will arrive later.
AMD is pretty quick maybe end of this year, it all depends on what AMD does. If 8000 series makes its debut this year then Nvidia could paper launch but thats about it. 700 series will be launch probably second quarter 2013