If you've noticed that scrolling between chapters became more difficult after upgrading to iOS 4, you're not alone! Sometimes it could take two or three tries to get it to work.
As I've been working on the same kind of functionality in Reading Plans (in this case, side scrolling to go between different days in the plan), I got the chance to re-visit code I wrote in the early days for iOS 2, which also worked in iOS 3 but seemed to deteriorate a little in iOS 4.
I'm happy to report that I've been able to make adjustments for much easier side scrolling. This will be included in the Reading Plans update that I hope to deliver to the store within a couple weeks.
Thank you to Matthew S. for putting the bee in my bonnet at exactly the right time!