Apple's informational page about its iBook feature on the iPad promises that you can have the book read out loud to you by the iPad. Apple says, "iBooks works with VoiceOver, the screen reader in iPad, so it can read you the contents of any page."
Amazon.com was forced to allow publishers to turn off this technology on the Kindle so it is unlikely Apple is going to get away with it on the iPad. The publishing industry will likely see it as a copyright infringement of audiobooks. Wired' Threat Level reports that the Authors Guild's executive director Paul Aiken said of the Kindle's feature in February, 2009, "They don’t have the right to read a book out loud. That's an audio right, which is derivative under copyright law."
It will be interesting to see what happens between publishers and Apple over the iPad's VoiceOver feature.