Virtual Machine are one of the tools that a developer absolutely needs for
its work and the possibility to host different operative systems on the same
machine is a need that the modern era of computing have always more
frequently.
One of the hottest questions that comes on the air when the first releases of
Longhorn were out in the past (ops, should I say "Vista"? 
)
was something like this: Windows in the future will have a virtualization
engine integrated into the OS core or not?
The answer is not clear yet, but Microsoft is taking virtualization in a
serious consideration. Rumours on the air now seems to say that Microsoft could
release a Windows Vista version with a bundled Virtual
PC, but nothing about integration of a virtualization layer on the OS
core.
Maybe it couldn't be an integration that will be possible soon (expecially on
the client side) but a future "Vista Server" (or how it will be called the
Server-side version) must have something like this. If we want to have a
revolutionary platform, this is a feature that must be added.