F2thaK at talk.maemo.org has put together a how to on speeding up transitions for the N9. I’ve not had a problem with how the transitions themselves, I think they’re extremely well times to direct the user as to what is happening on the screen.
As recent anecdotal example, our smartphone nOOb, Steve commented on smoothness of the 800 vs 4S. They are actually just as quick as each other except the animation of the 4S keyboard you can see rotating on screen whilst the 800 dips under and reappears. It’s better than a sudden landscape/portrait switch.
Source My Nokia Blog