eggs in one basket
its all fine these companies saying that virtualisation reduces cost, - yes in terms of hardware, but the more load you put onto a system the more power its going to consume and the risks of wear failure is greater.
Perhaps in large companies this may work, but for companies say less than 1000 users I don't think its viable.
With the best will in the world, having everything on one machine gives no redundancy, so then you buy 2 servers. Hmmmm, wasn't we trying to get away from that?
We have dabbled with Server 2008 / HyperV and felt that all it was, was virtual PC on drugs. not a platform for running multiple O/Ss on.
Jeez, imagine the I/O troughput to the hard drives - the heads would be constantly thrashing.