Hybrid SLI is a new technology that will allow you to run your graphics card in SLI mode with the MCP72's integrated graphics chip. There aren't any benchmark results available yet but according to some leaks Hybrid SLI will offer a performance boost of 5-40%, depending on how powerful your graphics card is.
Systems with high-end cards like the GeForce 8800 series will only see a performance boost of about 5% while people with low-end graphics cards may experience boosts of up to 40%.
AMD's RS780 will compete against the MCP72 but the RS780 will arrive two months later, in November.
Source: OCW