I'm building the mother of all VMware ESXi 4.1U1 servers, based on the new Z68 chipset. The goals are reasonable cost, efficiency, and a lot of flexibility and coolness (literally and figuratively).
A nice bonus is VT-d (VMDirectPath) support, where worry about what components are not on the VMware HCL are greatly lessened, since such devices (like USB 3.0 controller) can be passed through to the Virtual Machine. This could be used for a VM to be allowed to see a Realtek NIC that ESXi itself cannot identify, without tweaking the hypervisor (generally not a good idea). Or it could just be used to allow full speed USB 3.0 support for a VM running Windows, for much faster copying.
In a nutshell, ASUS P8Z68-V PRO board doesn't yet support VMDirectPath, but apparently, the MSI Z68A-GD80 (B3) does.
I'm also excited to say I've been getting some excellents results for disk throughput tests underway: stay tuned for many more details on this rig, and screenshots and videos, coming to this site throughout June!
EDIT added 7/15/2011:
You may wish to check out updated info at tinkertry.com/vmdirectpath
turns out the ASRock motherboard supports VT-d as well!