Update. Since the publication of Jerry Griswold's evaluations of e-readers and the picture book (at the very bottom) a number of other writers, publications, and experts have weighed in on these topics--most recently (4/22/11) in the Op-Ed pages of the New York Times in an essay by Lawrence Downes, "The Children’s Book Comes to Life Electronically. Should We Be Alarmed?": http://www.nytimes.com/2011/04/22/opinion/22fri4.html
"Examining E- Picture Books," Maryland Morning: http://mdmorn.wordpress.com/2011/02/18/218113-examining-e-p/
"The Best Children's Books on the iPad," New York Times: http://gadgetwise.blogs.nytimes.com/2011/03/28/the-best-childrens-books-on-the-ipad/
"Children's Book Apps," NPR: http://www.npr.org/2011/03/28/134663712/childrens-book-apps-a-new-world-of-learning
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Jerry Griswold writes . . . "When folks talk about e-books, they are mostly thinking about offerings for adult and young-adult readers. These e-texts consist mostly of words and all that’s needed is a black-and-white reader; Amazon’s Kindle (currently, $139-$189) is a popular device in this category. But children’s picture books present a greater challenge since what’s needed is a more sophisticated device that can display color and images. At the moment, there are only two readers that can do so: Apple’s iPad and Barnes and Noble’s NOOKcolor...."