Vmware, a popular developer of virtualization software, is calling foul on the recent deal with Microsoft and Xen to allow virtualized servers to run on Windows. Calling it a "one-way street", Vm points out that the agreement only allows Linux to run on Windows through Xen, not the other way around. Of course, it doesn't mention that Vmware won't be virtualized in any way, shape, or form under the agreement.
Is it a slippery slope? Could be, could be, Microsoft is certainly adroit at getting in the thin end of the wedge. It could also be a misdirection to expand into other turf of other competitors, say, Google.
My guess is that this is going to open up a Pandora's box where something totally unexpected is going to happen, because virtual environments promote these sorts of things. Someone is going to find a twist that completely subverts the intentions of this deal. What will it be? I don't know. Maybe someone finds a bug. Maybe Apple, maybe Vmware, comes in with a great idea that uses the technology to host iTunes, or World or Warcraft. Who knows, something. Something unexpected. Watch this space.