The nForce 500 series will support both the Intel Conroe and AMD Socket AM2.
nForce 590 will be the highest performance NVIDIA chipset for AMD AM2 and Intel Socket 775. The chipset will be specifically tweaked for SLI and Quad SLI and feature a new technology called "Link Boost." Link Boost will, supposedly, offer increased bandwidth between GPU and MCP if, and only if, the system uses NVIDIA-only components. Currently, only the 90nm GeForce series graphic cards will support Link Boost, but future high end cards will as well.More details over here.
The nForce 590 SLI, 570 SLI and 570 Ultra chipsets also features an option called "FirstPacket." FirstPacket apparently is NVIDIA first attempt at packet prioritization, or Quality of Service on the NVIDIA firewall. The new chipsets will also feature a "teaming" feature that will allow for some rudimentary traffic shaping while using both Ethernet connections on the MCP.