IPad 3 wifi only: Keyboard lag is intermittent but generally ok. Worse than ios 6 but usable.
Screen rotation is very jerky
Four finger pinch to desktop animation has awkward abrupt ending
Parallax effect jumps and starts, so I turned it off.
These are all things I can live with...
BUT what I absolutely can't live with is the awful performance with photos and wallpapers!!
From a photo in the Photos application (taken with ipad camera), it takes 4-10 seconds to bring up Share options
Choosing "set as wallpaper" takes another 5 seconds
Once in the move/scale screen, pinch to scale causes it to freeze nearly immediately. If I wait it will unfreeze after 10-12 seconds.
Setting both lock and home screens to use this image takes 13 more seconds.
The same applies to Apple's built in static wallpapers. Unacceptable. A 16MP high quality JPEG? Forget about it.
Not to mention that buttons in the ui don't light up when you press them, so during that 13 second wait for the wallpaper to set, I'm not even sure I pushed the button!!!
Honestly, this reminds me of my first Samsung/Android phone. Very rough around the edges.