> Maybe the only transparent/alpha effetcs are used by the system menu
> and the Polynet dock

AFAIK, PolyNet uses fake transparency instead of real transparency (alpha compositing), so there's not much to calculate for the CPU anyway.

> the Powerbook installation is a mirror copy of the one present in the MDD HD
> and there is an huge difference in speed/smoothness.

That may be solely due to the R360 being faster than the RV360 in pure 2D operations like window moving/resizing. What I (and Jim) have been referring to specifically are effects using 2D operations which are normally calculated by the 3D part of the GPU but have to be calculated by the CPU as long as the needed functionality in the driver is missing, such as transparency done using alpha compositing. The question is whether or not such effects are rendered significantly faster with a faster 2D GPU. I'd like Lucy be taken as a yardstick because it makes intense use of this effect and also because it was reported to be unbearably slow on the PowerBook in that other thread.