We have SCCM 2007 with 11.000 clients and many DPs, PXE sveirce points, etc. virtualized (except the database which is not virtualized because of VMware licensing costs, it has 32GB of RAM, it would consume too much from one host) and it works very well. Maybe it wouldn't work on well HyperV :).I/O requirements are quite low, ~200 IOPS during normal usage (the management point and primary site server are on different VMs).CPU usage is also moderate, I see spikes to ~30%, average 5% out of 5 vCPUs (2 for MP, 3 for primary site server).