Source:
The rumor feed
It looks like the GT300 will be the first Nvidia card to do DX11, and ATI will be there first with their RV870 Radeon 58XX series.
ATI will have a few months lead over Nvidia in the DX11 department and may have superior hardware as well.
What do you guys think of Nvidia's slacking lately? I don't consider myself a green fanboy but I did prefer Nvidia cards until they started to re-brand their chips with only slight or no architecture changes.