I've got it working - still quite buggy and getting LOTS of errors, etc. but 100% working.
65 VMs that I'm doing load testing, migrations & failover testing. The only thing I can't do (yet) is Volume License and activation/deactivation type testing because this W8 is self-activating.
How I did it:
Build VM in Workstation 8.0 (edited the config.xml file so that it says "windows 8 x64", etc.)
Migrate from Workstation 8 (with VMware Tools installed) over to XenServer
Migrate from XenServer over to Xen XCP
Migrate from Xen XCP over to vSphere 5 / ESXi 5
No idea why or how it worked but it did. I had read a few blogs of people saying that they got it to migrate directly from XenServer over to ESXi 5 but I couldn't make that happen. I tried to build it on XenServer and just install VMware Tools but that didn't work - I think it really liked being on a HV where VMware Tools were installed & running.
Also, FWIW, I kept EVERYTHING on the same hardware - Built on Workstation8 on Dell T5500, Migrated over from Workstation 8 over to XenServer on another (identical RAM, CPU, HDD, etc. same type & brand parts not just "matching specs") T5500, over to Xen on a third T5500 and then finally over to ESXi 5 on a 4th T5500.
I had problems changing even types of CPUs. I could only get it to work if I kept the same exact hardware even across the board. (fwiw it was on Xeon X5680 CPUs & Samsung 8GB ECC ddr3 RAM with a single old-school 300gb raptor). Dell's T5500 BIOS version A11.
If you PM me I can build another one on a really small HDD and then host (is that legal/legit?) the files for someone who wants to try a short-cut.
I'm now able to migrate W8 across heterogeneous HA clusters & resource pools... and even directly from one machine to the next (like a T5500 with Xeon 5600 CPU to a T5500 with 5500 series CPU or even to T7400 with dual 5400 Xeons).
Again, assuming this is legal & legit (I don't see why not), I have a ton of either old 40-80gb HDDs or 32GB USB sticks. If you want to paypal me something reasonable I'm happy to back up a clean VM install and post it to you.
I'm having immense trouble with vMotion - I can't seem to migrate a W8 VM from one HA cluster over to another HA cluster (realtime with no interruption to the end-user). I have no idea why but if anyone has some advice I'm all ears.
What I get is essentially a system config change and/or driver install requiring a reboot. Which is really annoying.
Also - for the guy who asked about >2 socket support in W8 - everything blows up and goes straight to hell when I try and migrate those test machines with 4-8 sockets. It goes into BSOD and gets past POST but then I get a random watchdog error and auto-shutdown. IDK if that helps you at all - because if you do a physical install it **seems** as though that would work but ymmv.
Happy to answer questions - hopefully some of mine will get answered too.