http://windowshelp.microsoft.com/communities/newsgroups/en-us/default.mspx?dg=microsoft.public.windows.vista.general&tid=dba63136-d282-412a-852b-2975b111b921&lang=en&cr=US&p=1

Andre,

I don't think so, I belive Vista can have a perfectly smooth 3D desktop
experience on less performant 3D accellerators if we loose the blurred glass
effect. Shadows and "compositioning" is a piece of cake for all recent 3D
accellerators, but the blurred glass effect is a pixel shader 2.0 microcode
program.

They could make a XP like interface that would be faster and take less system
memory then Windows XP if the wanted, the programs GUI elements would float
around in hardware accellerated heaven on the GPU and its memory. Oh well.