I've got the Amazon app for my iPod touch. Quite frankly it is nothing to get excited about. Very lackluster compared to reader apps available for years on PDAs, smartphones, and Windows PCs.
The true test will be in the iPads screen quality in various lighting conditions, the ease or lack thereof of transferring non-DRMed books to the iPad, its ability to read ePubs, its actual battery life under reading conditions, the number of book formats that are readily available, and the final cost with tax and accessories compared to real tablet computers of the same size.
I'm skeptical to say the least.
I think you could take a pile of monkey poo, paint it, slap on an Apple logo, and a million applephiles would pay hundreds of dollars for it sight unseen.