Hardware Requirements for a VM Centric Workstation?

I really have more than one question and this may be too large a topic:

  • Do you use virtual machines in your daily routine and for what tasks? 
  • Which OS do you use as a host?
  • What hardware would you recommend for a VM centric workstation? (I'm a developer and would like to be able to play with or use for VMs for different projects in the future).
  • @Wendell: You hinted a few times that you use VMs. Can you go a little bit more into the details? Do you "script" your VMs and if so, how?

Thanks & keep up the good work!

Greets from central europe!