An
article in the Independent today, discusses the development of children's books on the iPad. It includes the interesting statistic that Apple are selling 77000 ebooks per day.
As they are selling ~1m iPads per month, which is about 33000 iPads per day, it's not clear whether this is people buying a couple of books for their new device, or a long-term trend. They have also released iBooks to their existing user base for iOS (they ask explicitly if you want it in the app store, rather than waiting for people to discover it), which is another 100m new users in the same time frame.
So, I'm not sure what to make of these stats yet, but it's interesting.