Part of the problem Microsoft bumped into with Vista, was hordes of people who had grown too attached to XP.. It seems they learnt their lesson (and found a cheap way to maintain backward compatability without having to keep legacy code forever). [XP with SP3 as a virtual-pc virtual machine within Windows 7]

We thought we had problems classifying client side bugs that required user intervention (remote? local?), what happens when a remote in XP-SP3 allows one to execute code in the Windows7 machine through local VM breakout? (indeed a new acronym is needed in anticipation: RAXPLVMB??)