"AI Overclocking" is the name Asus has given a feature in the BIOS that allows you to overclock your system by either 5%, 10%, 20% or 30% by changing only one setting. I can pull off a 5% overclock, but can't go any faster than that, and I suspect it's because my DDR400 memory is holding me back. This scenario is the only scenario I can think of where faster memory (DDR433/DDR466) might come in handy.
As far as "MAM" and "PAT" go, here's the deal: At birth, the 865 and 875 chipsets are identical. Intel tests them using aggressive memory timings -- the ones that run stable become 875s, the ones that don't become 865s. Now, many times what ends up happening is Intel needs more 865s than 875s (based on what the market demands), so they take perfectly good 875s, they "castrate" them, and mark them as 865s. Engineers at Asus and Abit have both found ways to bypass Intel's aritifical speed-limiter, allowing the 865s to run just as fast as the more expensive 875s.
Asus comes out and says that the P4P800 with the 865 chipset now supports PAT, which pisses Intel off because motherboards with the 865 chipset cost $50-$60 less than motherboards with the 875 chipset. Intel tries to do some damage control and comes out with a statement that PAT cannot be supported on boards with the 865 chipset because it's "hard-wired" into the 875. Asus -- presumably in an effort to avoid a lawsuit from Intel -- simply renames PAT, and instead calls it MAM on boards with the 865 chipset.
I saw a few posts from real Intel zealots saying that the 865 is inferior because it failed Intel's speed test -- Asus very nicely walks around that problem by saying that it has thoroughly tested MAM on its 865-based boards, and can guarantee reliability based on strict quality control standards. I've had the board for a week now, and having been very happily running my CPU at 1000FSB (250 x 4) with no difficulties of any kind.
I took a quick look at the Asus website and noticed they took down most of the references to MAM..... I guess Intel put a lot of pressure on them to downplay the significance of their achievement. Intel must really be steaming, because simply upgrading your 865-based board to the latest BIOS (1007 for the P4P800 Deluxe, 1.3 or newer for the Abit IS7-G) gives you all the functionality of a board that costs $60 more. The only reason to buy an 875-based board is if you demand ECC memory support -- and unless you're running a server, you probably don't. Besides, you take a performance hit with ECC memory, so chances are ECC users aren't particularly interested in overclocking in the first place.