I upgraded to Windows Vista a couple months ago because I needed to experience it in order to write about it and understand what customers are going through.
My Thinkpad Z61t has been sluggish compared to running XP, something documented in the trade press. This morning I was looking at Task Manager to see what proceses were eating up CPU. A module called dwm.exe was consistently taking up 12% or so of CPU.
Turns out this is the Desktop Window Manager, which handles the transparency effects and other new features such as seeing a preview of a window by mousing over its place on the Taskbar.
I disabled the transparency effect and dwm.exe fell to using about 5-6% of CPU.
As it happens, I can't stand the transparency effect. It makes it harder to discern the top edge of the current window and it costs a lot of CPU. Others using or deploying Vista may want to try turning it off.
/rich