Expansion slots wise, users are given four PCI Express x16 slots, one PCI Express x1 slot and one PCI Express x4 slot. Of the four PCI Express x16 slots, the third slot is electrically x8 while the rest are x16.
As there are only 16 lanes dedicated to graphics, multi-GPU configurations are pretty limited. However, ASUS has plonked an NVIDIA NF200 bridge chip onto the Maximus IV Extreme to provide more PCI Express x16 lanes.
In order to avoid additional latency introduced (which affects performance) by a bridge, the PCI Express x16 slots have been cleverly routed: slots 1 and 3 are linked to the Sandy Bridge CPU directly, while slots 2 and 4 are linked to the NF200. Hence, the NF200 is only used when running a three-card setup in slots 1 (x8 CPU), 2 (x16 NF200) and 4 (x16 NF200). In a two-card setup, the 16 native lanes are split into twin 8-lane links between slots 1 and 3.
Stuff the board with up to four sticks of 8GB memory for a total of 32GB. Maximum memory frequency (or divider, rather) is 2400MHz.
Excellent contact between the motherboard components and the heatsinks.
This little guy here gives you the additional PCI Express x16 lanes you may need.
And this is the Intel P67 Express chipset, or Platform Controller Hub (PCH).