How cool it is to have 16vCPU in a VM for Fault Tolerance? I remember when first introduced, FT had the same magic as vMotion. But limitations to 1vCPU VMs and other limitations concerning backups were factors that this feature is not widely uses, even if the configuration at the vSphere level is minimal.
For the use cases that needs 16 vCPU in a VM that's certainly, but only VMs that really needs that number of vCPU orhterwise you'll waste CPU cycles. I've listed on my VMworld 2013 page many free VMworld sessions. One of them is a very cool VMworld session about Fault tolerance showing the possibility to configure 16 vCPU in a VM to be protected by Fault Tolerance.
Fault Tolerance, as you probably know provides continuous availability. It offers zero downtime, zero data loss, there is no temporary TCP disconnections.
FT is complete transparent to guest OS, which don't know that is actually mirrored and that there is another (shadow) VM following in vlockstep few milliseconds behind what's happening in the protected VM.
FT protects VM, which survive server failures. FT requiring absolutely no configuration of the Guest OS or the in-guest software. (Right click VM > FT > Turn ON FT…)
During the session they do a live demos to showing the configuration the specification of different VMs and in one of the demos they SSH into the VM to show that the VM is actually configured with 16 vCPUs.
It's probably one of the coolest features that exists for 1vCPU VMs since first introduced in back vSphere 4, and the barriers of the multi vCPUs are perhaps just being lifted.
During VMworld Barcelona I have actually seen this session and I had the feeling that for them it wasn't a problem to implement multi vCPU VMs in FT configurations, but perhaps (it was my feeling) that the underlying hardware has to be very powerful in order to cope with such a config.
There will be some requirements :
While the feature is a tech preview, it's possible to review the VMworld 2013 session for free through this YouTube video. It's a full 1h session. BCO5065 – VMware vSphere Fault Tolerance for Multiprocessor Virtual Machines – Technical Preview 
– Jim Chow (VMware), Wei Xu (VMware)
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Just to note: in official Vmware documentation (vsphere-55-configuration-maximums.pdf) there is still noted, that FT can be used with only one vCPU.
Regards, Dejan
Just to correct my self … this features is not yet included in new ESX 5.5, but it will be soon, I believe.
It’s Tech Preview. I think that it might be part of the next major release.
In vSphere 6 or maybe 7 i believe.
Well, finally it looks like it will be 4 vCPUs for ESX 6, so no 16 vCPUs for the time being.
In any case, 1 vCPU is a little too less, but 4 vCPUs are good enough for most production VMs.