There have been a few reviews of the leaked Windows 7 Beta which questions the usability of the Windows 7.
In my opinion, one of the biggest questions for the upcoming OS from Microsoft is the compatibility of Windows 7 to previous applications that have existed even before and the early days of Windows XP.
I have not been a Windows Vista fan, nor have I used Vista ever. I have had some few experiences though with Vista when some of my friends ask for help with their PC running in the Windows Vista platform.
Compatibility, one big thing that made Vista flop. Don't ask me, but at the early days when Vista was still named as Windows Longhorn, I was anticipating on upgrading from it, but I was really disappointed with its incompatibility to many certain applications that it would render most of the applications I use daily, useless. I have a laptop that is specifically made to be ran under Windows Vista, but I ditched it and reinstalled my Windows XP on it, because I am more focused on usability against aesthetics.
With Windows 7, compatibility is out of the question, but rather its usability to old school Windows XP and earlier ...