I was never happy with the smoothness of image scrolling in Jaipho. But the current engine was usable enough, so I was holding the issue to be solved in some better times.
After iPhone 4 was released, I was surprised with bad performance on it too. iOS 4.2 update made things even worse. Image scrolling on iPhone 4 is worse than on any other iPhone!
Recently I started to work on Jaipho 1.0 which should be out in September or October, and the smooth scrolling was one of the first issues to start with.
Every class is in it's own separate file. From class name you can figure in what folder does it resides (php Zend framework users will be familiar with this). Example: JphSlider_Slide is placed in the /Jph/Slider/Slide.js file.
On http://jaiphodemo.info/demos/ipad-test-01/ you can find the first test version. If it is accessed by iPad it will be optimized for it. All other devices will be served with iPhone optimized version.
This iPad version is mainly made by following the guide published on Porting Jaipho to iPad article.
I'm currently working on Jaipho version that supports iPad. As iPhone 4 is released in meanwhile, including it in a release seems to be very reasonable.
As I red on the net, there is a certain possibility that Jaipho works just fine on iPhone 4, no matter because they have different screen resolutions. There is a excellent article about iPhone 4 resolution on daring fireball - Why 960×640