I am planning upgrading our D3Linux system and the hardware it runs on.  I am considering setting it up to run on a RHEL virtual machine with the hope that future major version upgrades might be easier on the same hardware.

Are there any major cons of running in a VM?   

Any configuration and setup tips are welcome.

Hy 
i've being runnig D3 over an XEN machine... with CentOs with VM servers... an few hints i can give is about the disks ... make at least 3 storage, 
1 for SO ( just the minium disk space)
1 for userdata and backup ( it depends how big your d3 data is, and how users use the linux server)
1 for D3 data
with that structure... if your SO crashes... you can create only a new disk for SO, and atached the other 2 disks
and when i see i had an stable env, i stop the d3 vm machine, shutdown the VM detache the userdata disk and d3data and take an snapshot only from the first disk, then i reattached the others disks and start all the service... with that in case some crash or so update error.. you have fast recovery 

I am planning upgrading our D3Linux system and the hardware it runs on.  I am considering setting it up to run on a RHEL virtual machine with the hope that future major version upgrades might be easier on the same hardware.

Are there any major cons of running in a VM?   

Any configuration and setup tips are welcome.

I am planning upgrading our D3Linux system and the hardware it runs on.  I am considering setting it up to run on a RHEL virtual machine with the hope that future major version upgrades might be easier on the same hardware.

Are there any major cons of running in a VM?   

Any configuration and setup tips are welcome.

Thought I would quickly add that Virtual Machines are great in many ways!  As already mentioned you can move the virtual disk to a development machine and have a snapshot on dev in a matter of minutes.  Also the disaster recovery of the machine is great when you keep a offsite backup of the virtual machine.  We have run D3 in a VMWare environment for years. 

Works Great

I have run D3 on MS Server hosted on MS Hyper-V for more than a decade. I don't expect to ever go back! As already stated, it provides many advantages, and I have noticed no difference from running on tin. Depending on what you want to do, integration with other hardware might be a challenge, but I have never struck that particular problem.