My user experience between the os's
XP-> Vista
-Great folder browsing in explorer
-First time I've actually used the inbuilt 'music', 'pictures' folders, due to the new locations and customisability of them
-Nice to have the preview window when hovering over a taskbar item
Vista->7
-Libraries are a great long needed addition to Windows
-UAC barely noticable, and tweakable
-Awesome keyboard shortcuts
-Easier to work with by tiling windows quickly to the left/right side of screen
-Can now view previews in full screen for each window type.
--ie, if you have 5 explorer windows open, clicking on the single explorer group will give you the option of 5 previews to choose from
Productivity is improved from XP>Vista and more so ni Vista>7
Anyone shunning 7 clearly hasn't used it as their main OS to actually 'do' things on the machine.
After using Vista, I would still go back to XP without missing too many features.
After using 7 however, I've not even booted my XP64 partition once (or the Vista one)
I'll be buying 7 on release