From Walter Mossberg of the Wall Street Journal:

The iPad is much more than an e-book or digital periodical reader, though it does those tasks brilliantly, better in my view than the Amazon Kindle. … I consider the larger color screen superior to the Kindle’s, and encountered no eye strain. … The iBooks app also lacks any way to enter notes, and Apple’s catalog at launch will only be about 60,000 books versus more than 400,000 for Kindle.