btw, the transition effects, the floating icons, desktop sliding effects etc are all done in 3D and by the GPU and not the CPU. The GPU on the N900 is as fast iPhone 3GS if not double the speed. So obviously the issue isn't with the hardware. It's all software.

Well, if you get N900 to only run 1 app at a time and never multitask, it's actually pretty darn smooth. The task witcher animation is smooth, launch/close app transition animation is smooth. Might still not look as fluid as iPhone but I think that's just a different in animation quality or framerate and not a fault with hardware.

I reckon it's just not prioritised well enough to "always" be smooth.