Because SLI installation methods will be slightly different from manufacturer to manufacturer, its important to take a look at the process on each board and see if its too complicated or causes any problems.

The naked NF4 SLI-DR motherboard.

After installing the first NVIDIA 6800 Ultra GPU, its obvious that we are going to have to UN-install it to make the necessary SLI adjustments to the jumpers underneath the GPU heatsink. 

Using the jumper removal tool provided by DFI, you have to go through each of the banks of jumpers and move them one position in order to enable the SLI mode on the PCI Express slots.  There are six banks of jumpers to do this to and should take you less than a minute to complete. 

And now they are all shifted, ready for the graphics cards to be installed.

That is two 6800 Ultras, with the DFI SLI connector attached to the cards for data transfer and card stability.  Notice that you do in fact lose one of the standard PCI slots to the massive GPU heatsinks. 

Note how close the PCB on the graphics cards comes to the top of the heatsink covering the nForce4 SLI MCP.  This is not a trait of this motherboard, rather a trait of the entire chipset.  Maybe this explains the move BACK to two chipsets with the upcoming Intel nForce platform?