The Building Windows 8 blog has plenty of interesting posts on how Windows 8 will look and behave. Many of them also detail why particular design choices were made.
I have noticed an interesting trend in those explanations. They usually explain how user behaviour changed from the beginnings of Windows until Windows 7 and use that as the basis for upcoming changes in Windows 8. E.g. it has been noted that the taskbar has become the primary program launcher in Windows 7 as opposed to the Start Menu in earlier times – the Start Menu instead was only used for rarely-used programs.
The problem I see there is that (depending on who you ask) between 25 and 45 % of Windows users are still on Windows XP. If many major design changes in Windows 8 are done in response to how user behaviour has changed with Windows 7 they probably provide upgrading Windows 7 users with a natural progression. But many people skip one or two Windows versions (Windows XP usage dropped only slightly with Vista but dramatically with Windows 7) and Windows XP is close to its end of life. So it is natural to assume that many XP users will switch to Windows 8 once it hits the market. But while some changes may be gradual when going from XP to 7 to 8 they might be much more abrupt when going directly from XP to 8, skipping Windows 7 which introduced users to some concepts that are expanded and built upon in Windows 8.
I wonder whether they take that into account when designing the new OS.