Microsoft does heavy optimization for Windows OSes (see http://blogs.msdn.com/virtual_pc_guy/archive/2004/11/05/2527...). Windows 7 is also quite fast on its own on modern hardware, even if it can't stack up against XP on 2001 machines. I don't think it's too much of a stretch to see people using this technology regularly and seamlessly, especially since third-party companies have been doing this on the Mac for years.
