I use virtual machines for testing and scanning other subnets that I don’t want on my main machine.
We use virtual machines mainly for testing purposes too, but have configured VMs for some users that need to run some legacy applications that don’t run under Vista as well.
We have used desktop VM for some time both in system and UA testing. We’ve set up our EXi and ESX as dev/testing and staging/production respectively. However, if you are asking have we converted our users to all VM at the desktop – no. But we have designated some VM for UA as appropriate.