There is another thread in which this is discussed. If you are jailbroken, you can open springboard.app and there is a .plist in that with settings for the springboard. The file changes depending on your phone model; for iPhone 4 it is N90AP.plist. In this there is a setting:
<key>launch-mode</key>
<string>pre-animate</string>
Removing both makes opening animations smooth again. Seems they added this to make apps NOT wait for the animation to finish, which makes it choppy.
<key>launch-mode</key>
<string>pre-animate</string>
Removing both makes opening animations smooth again. Seems they added this to make apps NOT wait for the animation to finish, which makes it choppy.