3d accelleration to make your 2d desktop run faster and smoother? BLOODY BEAUTIFUL.
3d Desktops? BLOODY AWFUL.
Look, as long as your interface to the computer consists of a mouse (which is, essentially a 2d device) and a keyboard and your display is a screen (a 2d device), 3d desktops are going to suck donkey bollocks. Every single way you can describe a 3d desktop maps directly to a 2d display with virtual desktops--which have been about and working at decent speeds since the days of the 386. Making it 3d only makes it less efficient, harder to find things, and more confusing for anyone who isn't a geek.
Before anyone even contemplates switching to 3d "desktops" (even the word "Desktop" is mired in 2d thinking!), a full on 3d input and display system is required. Even then, applications that need 3d displays and input need to be created. Everyone and their brother isn't hacking on something in Lightwave, but you'd be hard pressed to find someone who didn't use IE, Word, Excel, and the like.