I used to work with Virtual PC 2007 and Virtual Server 2005 for a time being; but since I had to start developing my skills on CentOS I was suffering from the speed of Virtual PC 2007 on my Windows Vista Laptop which was from the great range of T7500 series of Intel CPUs. So I was sure about the hardware but not the virtualization platform; I decided to give VMWare Workstation a try yesterday (VMWare 6.x does support Windows Vista as host and also supports both 32bit/64bit operating systems both as host and guest OS).
VMWare Workstation was just faster even double than Virtual PC specially when it comes to resource usages... I hope these issues would be solved and we see a better performance specially in Hyper-V as for the moment market leader of virtualization is VMWare.
I am thinking from yesterday to setup our Virtualized Servers on VMWare for the time being but not sure yet.