I agree with Brian on the 5 per core.
Our production VDI consists of 80 users per ESX host on IBM 3850 Quad Quad Core with 128 GB of ram, quad quad port nics (we also vacilate anywhere from 60 - 100 powerd on vms) hardware.
VMs per core: 5
Mem per VM: 768, 1, and 2 GB
VMs per vSwitch (each vSwitch contains four pNic (1 from each quad port nic)): 20