RD790 is AMD's top notch chipset and the final revision has finally come to the hands of motherboard manufacturers. The earlier revision was recently replaced with the new one, and the new one seems to be the final.
This means that the board will be sent to AMD for qualification in the next week or two and everything should be ready for the launch in middle of October.
Naturally RD790 will be Phenom or Phenom FX ready and supports both Socket 1207 aka Socket F and Socket AM2+ and there will be boards available for both sockets. AMD plans to introduce Phenom FX this year while the Phenom AM2+ are likely 2008.
Nvidia's chipset division will definitely be challenged with RD790 and its PCIe 2.0 and Quad Crossfire support but Nvidia will have its new chipset very soon.