FUD Zilla claims ATI's 40nm mainstream RV740 GPU will arrive in April:
ATI´s first 40nm chip might be ready as early as April. Obviously, the new 40nm chip has a bit more shaders than its predecessor, the RV735. ATI did a good job with its 55nm generation, and Radeon 4650 and 4670 are selling well, but not as good as Geforce 9600GT.
Nvidia hopes to bring out its 40nm chips at about the same time, but as far as we know Nvidia always starts its transition to a new process with entry level products, and it will get its mainstream competitor a bit later.