Tbd 1) if Apple will do something to slow or stop Kindle on the iPad, and 2) to what extent Amazon will offer functional parity (e.g., capturing annotations) between the Kindle devices and the Kindle client for the iPad
What's more, Amazon is years ahead of Apple in building relations with the publishing industry, being one of the biggest print-book retailers in the nation. Amazon now offers more than 450,000 e-books, and has access to more than 1.8 million free out-of-copyright titles. Apple has said it will start with 60,000 titles from five of the largest publishing houses.
For iPad's first year, at least, "it is likely that people will buy more books from the Kindle store than they will from Apple iBookstore," predicts James McQuivey, a Forrester analyst. "If you're an iPad buyer, chances are about 90% that you're also a book buyer on Amazon. Amazon has your credit card on file, they know what you like. ...That relationship is the key to selling books."