I've just started my quest to get this working. It's been difficult finding examples of success from others but I finally found a reference to a specific motherboard and CPU combo that has worked for others.
HomeServerShow
I'm using an Intel DQ67SWB3 motherboard with an i5-2400 CPU. Of course I had to get a separate Intel NIC since the onboard isn't supported.
My plan is to use this for a number of servers including my CCTV security camera system. This is using a PV-149 PCI video capture card which would have to be passed through via VT-d for the VM Guest to see it. I've successfully installed ESXi 4.1 update 1 via a USB key and I'm in the process of adding some VM's. A couple of issues have come up. First, I don't have performance stats updating in vSphere client. I'm not sure if this is a driver issue with the "unsupported" motherboard or if it's a problem with the ESXi install. I can see the overall utilization on the summary pages though so it's not like I'm blind. Also, I'm able to add devices via VT-d but it's not clear to me yet if I can pass-through multiple devices to a single Guest.
I'm installing XP in a Guest right now and as soon as that's done patching (lot's of patches) I'll be working on getting that capture card visible.
I also plan on running PIAF (Asterisk) and SageTV in other VMs. I'm probably going to need a really basic DNS server as well. At some point I might try passing through the onboard NIC to a firewall VM, perhaps PFSense or Untangle. Not sure about that yet.