XP and Vista
For one of the projects I’m working on, I’m setting up a virtual server for QA purposes. To allow testing, we created a virtual hard disk of each platform that we deploy our application on. Nothing else was installed on these images, except for the OS and (possibly) an associated version of Office.

The numbers say it all. Vista is at least 5 times the size of a comparable XP installation. And for what? Aero? This is why I’m sticking with XP for now.
Don’t ask me how the Vista image without Office is actually larger than the one with Office 2007, though…
Did you try running the “Virtual Disk Precompactor.iso” in “C:Program FilesMicrosoft Virtual PCVirtual Machine Additions” and defragmenting the VM? The kb article http://support.microsoft.com/kb/833138 goes over exactly how to use it. -Ian
No, but I’ll check that out.
This point was really just about the difference in size between the different operating systems. Not quite a scientific test, sure. Thanks for the link!