Project Butter is what Google has named the overall smoothening of UI in Android ver. 4.1 JellyBean. In my few weeks of experience with official JellyBean rom on my ASUS Transformer Prime, I can definitely say that Google slowly is developing the skills that Apple has under the sleeve for some years now.The overall experience has definitely improved. Every transition has been well 'buttered'. The reason Apple still has authority over this part of UI experience, I believe is because, it handles prioritization of basic UI related commands very strictly. The secret to this 'butteryness' lies in deceiving the user with a more superficial responsiveness.