As well as introducing a new overall system, these Core i5 CPUs are different enough to both Core 2 and Core i7 to require a new socket. Core i5 will now use an LGA1156 socket, which as you can guess uses 1156 pins. Unfortunately we can't show you the new CPUs or the socket (without its plastic cover) yet but we can say this much; it's about the same size as LGA 775 and uses the same pins-on-board, contacts-on-CPU arrangement. As such it wouldn't seem necessary to require a new cooler design but, apparently it does, so neither existing LGA 775 nor LGA 1366 coolers will fit these new boards/CPUs.
Specifically the difference is in the distance of the mounting holes, which are slightly closer together than LGA1366 but slightly futher apart than LGA775. This means there is potential to just get a new retention clip for your cooler rather than a whole new one, if it is a modular design. Otherwise, there will be a whole host of new coolers coming out that have adjustable mounts, like the Cooler Master Hyper TX3 we used in our testing.
Further to the changes in cooler mount and pin layout, the CPU retention mechanism has also changed and we think it's an improvement over both LGA775 and LGA1366. Instead of the locking arm and securing plate opening in different directions they now open in the same direction and the locking arm actually lifts the securing plate off and away from the CPU in one simple motion. It's both easier to open and to install/remove CPUs.
Looking in a bit more detail at the particular board we were playing with and Asus has put together, what looks to us like a near perfect design. As mentioned earlier there is oodles of space around the CPU despite the use of a hefty 12+2 phase power system. You might find the largest coolers interfere with taller memory sticks but most should be fine.
The I/O panel is also impressive with dual Ethernet ports, both optical and coaxial digital audio, as well as analogue audio mini jacks, a reset button and no fewer than eight USB ports.
The PCI/PCI-Express slots all seem to be sensibly spread out with no obvious possible clashes between long graphics cards and other components - mainly due to all the ports along the front edge being laid down flat.