What is the maximum number of physical cpu's (and more importantly, cores per cpu) that ESX 5 supports?
Use Case: 1 Server with 2 Intel 8 core cpu's. Will all 16 cores be utilized?
Terribly-worded question, and you've not done any research at all but anyway...
Both version 5 and 4.1U1 support up to 160 virtual cores per host - if you buy enough licences anyway, hyperthreading counts as virtual cores. But different licence version support different amounts of virtual cores, for instance the Enterprise Plus version of v4.1U1 supports 12 cores per socket per licence, while lesser versions support 6 etc. So if you bought 2 licences of Enterprise Plus v4.1U1 for your machine you'd be entitled to use 24 cores/48 hyperthreads per server. Version 5 is kind of simpler, in that two licences will support pretty much any number of cores, i.e. your 8 per socket but you're then limited by allocated memory per licence, i.e. 96GB of allocated memory on running VMs per Enterprise Plus licence, so 192GB for your server.
There's lots of other information to be read at vmware.com.
ESXi will consume as many cores as you throw at it, so long as they're licensed. I have some AMD 6172 CPUs on some of my ESX boxes, and those have 12 cores per CPU and they're certainly all being used. There are some theoretical limits, but they're not likely to be run into outside of specialized hardware situations.