When customers save an article with Instapaper, get a book in iBooks, or download a podcast with Instacast, they expect it to be there next time they launch the app. Even though it’s technically redownloadable, customers see that as their data — they put it there, and it’s theirs to remove if and when they see fit.
Read his post to see why iOS 5 is causing issues with apps like Instapaper.