I'm not one of the fortunate few who got an iPad Saturday. But I am lucky enough to know several generous people who took screen shots for me. I'm posting a selection of those screenshots as side by side comparisons of the Kindle, iBooks, and Kobo apps. BTW, if you want to take screenshots of your iPad, click here for the instructions. Pictures are after the break.
The first image shows the Kindle and Kobo bookshelves, and the second image shows 2 different views of the iPad bookshelf.
The second set compares the bookstores. The Kindle Store is actually in the browser. I like it, but it's really not optimized for touchscreens. The Kobo Bookstore and iBookstore are both in the apps.
The Kindle app and iBooks both support landscape and portrait modes. Unfortunately, the Kindle app doesn't have a multi-column or 2 page view. This is a deficiency it shares with the Kindle DX.