I hope I'm wrong, but I'm guessing there would be a problem with the Ubuntu X11 libraries or configuration not being optimized for the n900 graphics hardware (very slow). But if that's true, from what I can tell, the SGX API is available to anyone that dares, or maybe someone could just tweak xorg.config. Regardless, I'm optimistic that MeeGo will produce the X11 stuff we'll be looking for to use the hardware-accelerated window manager of our choice.