There is a really interesting article over here about ubuntu 9 compared to Vista and Windows 7.
http://tuxradar.com/content/benchmarked-ubuntu-vs-vista-vs-windows-7
They compared installation time. Ubuntu was faster.
Mouse clicks in the installation: Ubuntu had less.
Disk space used: Ubuntu used less.
Bootup: Microsoft was faster, Windows 7 being the leader.
Shutdown: Linux was faster.
IO: Linux was faster.
Python: Windows just about edged it.
In the real world it probably doesn’t matter, the vast majority of users will continue on with a Microsoft operating system because the software they want to run and have supported by their local IT team will make this easier. Interesting followup here:
http://www.tuxradar.com/content/linux-vs-windows-7
As an OS X user the “improvements” to Windows appearance is laughable still.